Calcareous Grit Research Articles

Digestion Rate of Limestone Force-Fed to Pheasants

Tests were conducted to learn the erosion (disappearance) rate of marked limestone in the digestive tracts of penned pheasants (Phasianus colchicus) force-fed known amounts. The erosion rate was progressive and amounted to approximately 46 percent in 12 hours, 89 percent in 24 hours, and 95 percent in 36 hours. These data show that all calcareous grit may not be detected by standard food-habits study procedures. This may explain why chemical analyses of principal foods of wild pheasants, as shown by a study of crop and gizzard contents, generally show levels of calcium much below known requirements for penned birds. This study was conducted to learn the rate of erosion of limestone grit through pheasant digestion and whether a true measure of calcium ingestion was detectable by standard food-habits study methods. The need for this information became evident during a study of foods and nutrition of the ring-necked pheasant in Missouri (Korschgen 1964). Chemical analyses of principal foods consumed showed consistently lower levels of calcium in average diets than growth or maintenance requirements established by Dale and DeWitt (1958) and Scott et al. (1958) for penned birds. The availability of supplementary sources of dietary calcium was indicated by healthy, wild populations in northwestern Missouri, but crop and gizzard analyses generally showed small amounts of calcareous grit in the daily diets.

The Influence of Calcium on the Distribution of Pheasants in Illinois

The role of deficient calcium as a factor limiting the distribution of pheasants (Phasianus colchicus) in Illinois was investigated by comparing the availability of calcium and its subsequent inges- tion by wild pheasants on an area (Neoga) of old glacial till originating from the Illinoian glacial age and on an area (Sibley) of more recent till originating from the Wisconsin glacial age. The amount of calcitic grit, and the amount of calcium contained in the calcitic grit, collected from roads and agri- cultural fields on both areas were similar, as were the amounts of calcium found in the soils from the two areas. The amounts of calcium found in the grit from gizzards of hens and young from both areas were very similar. The number and hatchability of eggs per incubated clutch, the production of chicks per hen, and the ash content of femora and of entire carcasses of hens during the nesting season were similar among pheasants at both Neoga and Sibley. Wild pheasants, particularly hens and young, seemingly possess the ability to select (1) calcareous grit from noncalcareous grit, (2) calcitic grit from dolomitic grit, and (3) calcitic grit with a high calcium content from that with a low calcium content; this habit of selective calcium ingestion may allow pheasants to prosper on areas where cal- careous grit is found only in relatively small quantities. The availability of calcium and its subsequent ingestion by pheasants at Neoga, an area of old glacial till, are apparently adequate for the establishment of self-maintaining pheasant populations.

MICROPLANKTON FROM THE CORALLIAN ROCKS OF YORKSHIRE

Summary Assemblages of microplankton are described from the Lower Calcareous Grit, Hambleton Oolite, Osmington Oolite and Upper Calcareous Grit of Yorkshire. They consist of dinoflagellates and hystrichospheres. The hystrichospheres include new species of Micrhystridium and Pterospermopsis, and five species are described for the first time from Britain. Five species of dinoflagellates are described from Britain for the first time also. The stratigraphic distribution of species present is summarized.

The Lundy Complex: Its petrology and tectonics

The Lundy igneous complex projects through the Palaeozoic floor of the Bristol Channel at a point 24 miles due west of Ilfracombe, North-West Devonshire. Its subaerial part lies about the intersection of parallel 51° 11′ N., and meridian 4° 40′ W. Unique alike in structure and composition among insular masses of the Severn estuary, it affords evidence of former crustal weakness and associated vulcanicity in a region situated near both the northern boundary of the Cornubian Permo-Carboniferous igneous province, and the southern boundary of the Hebridean Tertiary igneous province. It is a composite block of alkaline granites intruded among contorted slates, altered calcareous grits and thin marbles, with a swarm of basic, intermediate and acid dykes cutting both granites and sediments in a dominantly north-westerly direction. Erosion of the resulting complex has reached a stage such that only Lundy Island, the central and eastern part of its rugged core, now remains above sea-level. This core rises abruptly from an irregular base of uncertain submarine extent to a maximum height of 47·5 feet above mean sea-level. From north to south its subaerial length is 3·1 miles; its average width is 0·6 miles, and its superficial area is nearly 1·7 square miles. Of the subaerial volume approximately 91·4 per cent is granite and microgranite; 6·4 per cent is altered sediment and 2-2 per cent is dyke-rock. The island is surrounded by an indented shore-line with steep cliffs, the latter being united to an undulating table-land at 350 feet above mean tide-level by

The Ammonite Zones of the Upper Oxfordian of Oxford, and the Horizons of the Sowerbys' and Buckman's Types

It is more than a century since J. and J. de C. Sowerby figured in The Mineral Conchology , from the Corallian of the neighbourhood of Oxford, the type specimens of Ammonites plicatilis, Am. cordatus, Am. excavatus, Am. vertebralis and Am. catena , and since Brongniart made the district the type and standard of the Oxfordian stage, a term adopted by Marcou and, after emendation by d'Orbigny, eventually disseminated in the stratigraphical literature of the whole world. Nevertheless, in spite of the time that has elapsed and of the labours of S. S. Buckman in the district, the precise stratigraphical horizons and ranges of the Sowerbyan types remain obscure, as does also the whole succession of ammonite faunas. This obscurity is reflected in the variety of interpretations that have been put upon the term “Oxfordian stage” (see Arkell, 1927, pp. 154–5). I accept here the scope of the stage as stabilized by d'Orbigny (1852, p. 522: “l'Oxford Clay, le Calcareous Grit, le Coralline Oolite de M. Phillips” [the last the Oxford Oolite of Buckland and Fitton]) in which form (including, of course, the coral rags) it has also been accepted by Dr. Spath in his latest comprehensive table of Jurassic stages (1933, p. 872). The Upper Oxfordian as there represented, and as now commonly understood, corresponds with the Corallian beds in England and the Argovian and Rauracian substages on the Continent. In this paper I attempt to show the content of the Upper Oxfordian, with special referrence to ammonite horizons, in the

Some British Trilobites of the Family Calymenidæ

I. Introduction The study of the Calymenidæ was begun with the re-examination of the figured specimens and described types of the British species, and the results of this work have already been published (Shirley, 1931, 1933). An extensive series of British and foreign specimens has been examined. It is believed that the results obtained are of general application to the whole group of the Calymenidæ or at least provide a basis for further research. Perhaps not the least interesting of these results is the discovery that certain species had wide geographical range but apparently a comparatively short existence. Such species are valuable for purposes of correlation over extensive areas. The mode of preservation of the trilobite test has a marked effect upon the ease of identification of specimens. The complete preservation of the dorsal test is relatively infrequent in the geological sequence of the British Isles. The greater proportion of the material is in the form of separated pieces representing the scattered portions of the cast tests or the broken remains of the test after death. This scattering of the parts often makes identification difficult. II. Preservation of Material In limestones and some calcareous deposits, such as the Silurian limestones of Dudley, Worcestershire, and the Ordovician calcareous grits of Hoar Edge, Shropshire, the test is preserved almost in its original condition. In some specimens the ornament is preserved in every detail, though too often it has been destroyed by the acid used to clean away the matrix. The best method

Societies and Academies

LONDON Geological Society, March 8. D. A. BRYN DAVIES: The Ordovician rocks of the Trefriw district, North Wales. The area described extends from Trefriw and Dolgarrog in the Conway valley south-westwards to Capel Curig. The Glanrafon beds are correlated with the beds immediately underlying the Snowdon volcanic suite in Snowdonia, and with the beds of the same name underlying the volcanic suite at Dolwyd-delan. The Crafnant volcanic series is considered to represent an incomplete development of the Snow-donian suite, the bedded pyroclastic and probably also the upper rhyolitic series being absent. In the neighbourhood of Dolgarrog, the Crafnant series is faulted against a thick development of pumice-tuff and spilitic agglomerate overlain by rhyolite-tuff and rhyolite. These are regarded as contemporaneous with the Crafnant series, but representing, in part at least, the products of a different centre of activity. The fauna of the Llanrhychwyn Slates, comparing closely with that of the Lower Cadnant Shales of Conway, places the underlying volcanic series in the Llandeilian, and indicates its correlation with the upper part of the Conway Volcanic series. V. WILSON: The Corallian rocks of Yorkshire. (1) The Howardian Hills. Three divisions of the Corallian are recognised and their stratigraphical relations are dealt with in detail. The important role played by the spicular remains of the lithistid sponge Rhaxella perforata Hinde in the building up of the Lower Calcareous Grit is recognised for the first time. Calcareous, and many varieties of siliceous, spicules are described, and their distribution is discussed. Though perfect lithological continuity exists between the Lower Calcareous Grit and the overlying Osmington Oolite series, the absence of any representatives of the Hambleton Oolite series and the Middle Calcareous Grit containing fossils characteristic of these two divisions is considered to indicate the existence of a non-sequence in this area. In the later stages of the Osmington Oolite period reefs became established, and numerous facies deposits accumulated from the erosion of the reefs. As the Lower Calcareous Grit passes gradually into the Oxford Clay below, so the Upper Calcareous Grit gradually gives place to the overlying Kimeridge Clay in the North Grimston district, there being no unconformity such as was formerly supposed.

Appendix II. NOTE ON THE STRATIGRAPHY OF ROULSTON SCAR

A short visit to Roulston Scar in December, 1917, yielded the following information :— (1) Towards the northern end of the Scar the break between the Calcareous Grits and the underlying Kellaways is sharply defined ; the Corallian consisting of a fine-grained non-ferruginous grit contrasting with the ochre-coloured Kellaways. Towards the southern end, however, this junction is not so readily seen, the lower beds of the Calcareous Grits being largely ferruginous. (2) The top of the Kellaways appears to be everywhere marked by a bed consisting largely of rolled fragments of Belemnites together with smaller nodules ; the nature of this deposit forcibly calling to mind the two beds of rolled fossils and phosphatic nodules in the Gault and pointing to pene-contemporaneous erosion. (3) The general section below the Calcareous Grits is approximately as follows :— Ferruginous sandstone, shrly in parts, crowded with water-worn fragments of Belermnites, apparently belonging to the following species : B. abbreviatus and B. oweni, 4 to 6 inches ; ferruginous sandstone, unfossiliferous, about 1 foot ; ferruginous sandstone, fossils abundant but very badly preserved, Trigonia allied to T. clavellata, Pecten inaequicostatus and P. demissus, Hinnites sp. together with a few fragments of belemnites and unrecognisable fossils, about 10 inches. [From apparently the same bed at the southern end of the Scar two species of ammonites were obtained ; these were sent to Mr. S. S. Buckman, who wrote— “Roughly speaking your Amm. show a Macrocephalites indicating top of the Cornbrash ( macrocephalus zone, base of the ...

The Table of British Strata

THIS table will be welcome to students and teachers, for the existing charts are now quite out of date. To compile such is a laborious and somewhat thankless task, for it is impossible to please every one; indeed, the authors admit that in two respects, retaining the Permian in the Palæozoic and placing the Wealden in the Jurassic, they “seek to assert general rather than individual opinion.” As to the former, the question seems to be largely one of locality; but in the latter we should have preferred the conservative side, at any rate till better cause is shown for the change; especially since it has led to the virtual suppression of the Neocomian as a system. For the same reason we are glad to see the Tremadoc group left in the Cambrian system. The latter they allow to be an important geological system, though we should have liked to see the alternative title, “Primordial Silurian,” entirely suppressed, for it is commemorative of nothing less than an unwarrantable usurpation. The authors include the Solva Beds of St. Davids with the Menevian, which no doubt is justified by the presence of Paradoxides; but in that case too small a thickness is assigned to the system, for this addition would make it at St. Davids over two thousand feet. Remembering its importance on the Continent, we should have ventured to exalt Rhætic, thin as it may be in Britain, to the dignity of a system, and we think that over much importance is conceded to the subdivisions of the Tertiary series. Are the Thanet Sands or the Oldhaven Beds—not to mention others—more important than the Lower Calcareous Grit or the Stonesfield Slate? Yet we find the former among Formations and the latter in Subdivisions. Does not the statement that the glacial deposits contain only derived fossils beg a disputed question? It would be well to add “slates” to the economic products of Charnwood, for the “honestone,” which is mentioned, is very local. A notable feature is the recognition as formation of Torridonian, Uriconian, Dalradian and Lewisian in the Archæan rocks, though some objection may be taken to the third name, on the ground that as originally defined it was a much too heterogeneous assemblage, and we may doubt whether the Moine schists, having regard to their history, form a good type. These criticisms, however, affect only points of detail, and some may even regard them as excellences, while as to the general excellence of the table and its high value to students there cannot be the slightest question.

Notes on the Coast Sections between Hayburn Wyke and Filey

The area to be visited during this Field Excursion consists entirely of beds belonging to the Middle and Lower Oolites. To the north of Hayburn Wyke are the Staintondale Cliffs, which are composed entirely of the Estuarine Series of the Lower Oolite, with the three marine divisions of the Eller Beck Bed, the Millepore Bed, and the Grey Limestone Series. The marine bands of the Millepore Beds and the Grey Limestone come to the shore on either side of Cloughton Wyke, where they form conspicuous reefs, which can be examined at low water. Between this point and Scarborough the coast is formed by the sandstones of the Upper Estuarine Series. At Scarborough the Middle Oolites first reach the coast and form the bold and prominent headland of the Castle Hill. This may be considered as one of the typical Oxfordian sections, nearly the whole of this series being exposed in a vertical cliff 250 feet in height. The summit of this cliff, with the exception of a thin covering of Boulder Clay, is capped by about 20 feet of Oolitic Limestone, representing the lower part of the Lower Limestone ; below this comes about 37 feet of Passage Beds very full of a small Ostrea, Gervillia aviculoides, and Pecten subfibrosus. These rest on 18 feet of soft sands with large calcareo-siliceous concretions forming the upper part of the Lower Calcareous Grit, the lower beds of which pass gradually down into the sandy shales of the Oxford Clay. By a fault …

On the Llandovery and Associated Rocks of Conway (North Wales)

I. Introduction, and Description of Area . The Geological Survey Map (Sheet 78 N.E.) of the district lying immediately south of the town of Conway reveals an outcrop of Tarannon Shales, which is curious as regards its relation to the associated formations, since the Tarannon Shales are represented as being both underlain and overlain by rocks of Wenlock age. This circumstance led us to examine this special area; and our attention having already been directed to the occurrence of graptolitic shales below the Tarannons in other parts of Wales, we thought it' possible that they might also be present in the Conway district. Our observations in that district have extended over a fairly wide region, including the greater part of the valley of the Afon Gyflin between Conway and Y–Ro; but the only area which we have mapped in anything like detail lies immediately south of the town of Conway itself, and occupies the hill opposite Conway Castle and the railway. This area is bounded on the east by the River Conway, and on the west by a fault (‘ boundary–fault,‚ as we term it in the following pages) which brings a calcareous grit of Bala age against Silurian beds.The northern limit of the area is formed by the Afon Gyffn, a‚ tributary stream of the River Conway, which it joins just below the Castle. The southern limit has been taken, for convenience, at the beginning of the dense woods belonging to Benarth Asylum. In other places higher up the valley,

On a new Genus of Siliceous Sponges from the Lower Calcareous Grit of Yorkshire

Nearly forty years since, Dr. H. C. Sorby, F.R.S., communicated to this Society a paper on the microscopical structure of the Calcareous Grit of the Yorkshire coast, in which reference was made more particularly to the nature of certain microscopic reniform bodies with which the rock ill places was largely filled. In mineral constitution some of these bodies were of calcite, others of chalcedonic silica, whilst ill others both these minerals were present, and the question as to their original constitution was decided by Dr. Sorby in favour of the calcite, since it was thought extremely iml;robable that, if originally of silica, this material would have been dissolved and replaced by calcite, whereas the substitution of silica in place of calcite was a well-known phenomenon. The definite tbrm and outline of these bodies left no doubt that they were of organic origin, and Dr. Sorby recognized their resemblance to the small siliceous globules which form an outer crust to many existing sponges, but rejected this view on the ground of their supposed calcareous nature, trod he finally concluded that they were small shells, possibly Foraminiferal, in whose inteiior calcareous or siliceous materials had been infiltrated, in the same manner as in the chambers of the Ammonites occurring in the same rock. Subsequently, in 1876, Prof. J. F. Blake, F.G.S., discovered similar minute bodies in rocks of nearly the same age in Dorsetshire and Wiltshire, and noticed that some of them were hollows enclosed by thin crusts or shells, which dissolved

The Upper Jurassic Clays of Lincolnshire

The broad tract of low country which extends from the Humber through the middle portion of Lincolnshire, and spreads out into the fen-country to the south, is underlain by a thick deposit of clay which, in the adjoining county of Cambridgeshire, has been called the “Great Fen-Clay“ * . The lower portion of this great pelolithic formation is undoubtedly of Oxford-Clay age, whilst its upper portion certainly belongs to the Kimeridge Clay. Owing to the absence of beds lithologically resembling those of the Corallian rocks of Yorkshire and the southern and south midland counties of England, no division corresponding in age to the Corallian has as yet been made out in Lincolnshire. Prof. Blake states that the Kimeridge and Oxford Clays here form one continuous formation †. In the Survey Memoir on this district it is mentioned ‡ that the Corallian group is entirely absent, and only the Oxford and Kimeridge Clays are mapped. Jukes-Browne goes still further, and states that “in Lincolnshire there is nothing to represent the Corallian group, the Oxford Clay merging gradually into the Kimeridge Clay“§. H. B. Woodward mentions that in Lincolnshire, Buckinghamshire, Norfolk, and probably Sussex, “the Kimmeridge and Oxford Clays come in direct sequence,“ and he adds that“ unless we imagine an unconformity— and there is no reason for this supposition—the Coral Rag and Calcareous Grit developed in Oxfordshire, Wiltshire, and Dorsetshire, are represented by portions of the Oxford and Kimmeridge Clays in the districts just mentioned“║. No attempt, however, has as yet been made to separate off a portion which would be equivalent to the Corallian of other areas. 3. Kimeridge Clay :— ( b ) Upper Kimeridge: thin papery shales, with Discina latissima . ( a ) Lower Kimeridge: dark clays, with septarian nodules, subdivided into:— (iii.) Clays with Amm. mutabilis, Astarte supracorallina , &c. (ii.) Clays with Amm. alternans . (i.) Clays crowded with Ostrea deltoidea . 2. Corallian . Black selenitiferous clays, with Amm. plicatilis, Amm. cawtonensis, Bel. abbreviatus, Gryphæa dilatata, Ostrea deltoidea , &c. 1. Oxford Clay , subdivided into five palæontological zones, with the Kellaways Rock at its base.

Notes on the Driffield and Market Weighton Railway

The construction of a new railway, however small, affords opportunity for fresh geological sections. In the present instance the line is only 13½ miles long, and presents no new features, but it is interesting in some respects, especially at its western end, where it shows the position of the chalk as regards the underlying beds. It was pointed out long ago by Phillips that a sub-cretaceous anticlinal existed somewhere about Garrowby, stretching east and west, which seemed to cut off the Oolitic rocks in North Yorkshire from those southwards about Market Weighton, but whether these rocks were removed by denudation previous to the deposition of the chalk, or thinned out against an old submarine shore-line was doubtful. The question is by no means settled yet, but the facts are these : the Lower Calcareous Grit and Oxford Clay of the Middle Oolites make their last appearance from the north at Hanging Grimston, near Acklam. The estuarine sandstones of the Lower Oolites share the same fate, except for a small patch at Kirby Underdale and Grimthorpe. These latter come on again south of Market Weighton. Between Hanging Grimston and Sancton the rocks, which underlie the chalk, are composed of Lower Lias, so that a vast gapappears. The mass of rocks, which constitute the moorland of North-East Yorkshire, consisting of estuarine sandstones, with their intercalated marine limestones, notably the Scarborough, Millepore and Dogger beds, which attain at the Peak a thickness of 600 feet, are wanting, as well as the Upper and ...

On the Corallian Rocks of England

I ntroduction W hatever may be the value of the grounds on which the ordinary line of separation between the “Middle” and “Upper” Oolites is drawn, there can be no denying that from the Oxford to the Kimmeridge Clays, in some parts of England, we have one continuous deposit, which, from a physical point of view, has been aptly termed a great “pelolithic” formation. During the period when this was being quietly laid down, at a quicker or slower rate, in these areas, other portions of the same great region were at various times subject to alterations of the physical conditions, in consequence of which the deposits were changed in character; they became Grits or Limestones, and supported coral reefs, with their accompanying Oolites. The very fact of these changes being local—a fact proved as much by the discontinuous as by the variable nature of the deposits—prevents our assuming that they were all contemporaneous, even in a large sense, as has been done by those who have used the term Corallian, as indicative of a period, for all or any of the coral deposits that have been formed between the commencement of the Oxfordian and the close of the Kimmeridgian epoch. In England, however, these rocks, originally called “Coral Rag” by Smith, from their development in that form in the area studied by him, have been divided into Upper Calcareous Grit, Coralline Oolite , and Lower Calcareous Grit , the classification being originally derived from Yorkshire; and it has been too hastily assumed that rocks

On the Relative Positions of certain Plants in the Coal-Bearing Beds of Australia

In the “Observations on the Flora of the Oolite,” by Baron de Zigno, published in the Quarterly Journal of the Society, No. 62, there is a paragraph respecting the supposed non-verification of certain genera of plants in the Australian coal-fields, which were reported by me in 1847. It is only right that I should offer a few words of comment on. that paragraph. By reference to the same number of the Quarterly Journal (p. 147), it will be seen that Mr. Selwyn has already recognized in Eastern Victoria “true Carboniferous plants;” and he further states that “in Tasmania the coal-bearing beds rest quite conformably on and pass downwards into calcareous beds, the fossils from which are, I believe, nearly all Carboniferous or Devonian forms.” Now this is precisely the case in New South Wales, in which colony the plants said to be Jurassic occur (coal-cliffs, Mulubimba, near Newcastle, mouth of Hunter River) in the same beds and blocks with heterocercal Fishes, one of which is figured by Dana as Urosthenes australis , and was acknowledged by Agassiz to be a palæozoic fish. In other portions of New South “Wales, and in the new colony of Queensland, in close connexion with calcareous beds holding abundance of “Carboniferous and Devonian” zoological forms, occur shales and fine calcareous grits charged with the plants which I reported in 1847, and which Baron de Zigno does not find verified by Messrs. Morris and McCoy.

On some Fossils from South Africa

Abstract A t the close of 1850 Mr. Stow and his party fell back into the interior to avoid the Kaffirs; in making the journey he collected largely the fossils on his route, and succeeded, with much trouble, in preserving them on his return. In a plain at the foot of the Rhenosterberg, a branch of the Sneewbergen Range (of which latter the Spitzkop is the culminating point), the author met with patches of ground strewed with nodular concretions and fossil wood (specimens 2 to 63) over an extent of about two miles in length and one in width. These fossils were on the surface, and had been probably derived from the neighbouring mountains. The plain was of a lozenge-shape, about twelve miles broad and twenty long; and was one of several of a similar kind that he had travelled through. It was bounded by the Rhenosterberg Mountains on the N.E., on the S.W. by a nearly parallel range, and on the S.E. was contracted to a narrow valley between low rocky hills. Two low volcanic dykes crossed the plain, one on the north-western, and the other on the south-eastern side. The strata forming the mountains are horizontal. There are about eight strata of sandstone forming the lower part of the Rhenosterberg. Immediately above there is a limestone full of rounded fragments of other calcareous and non-calcareous rocks, and sometimes containing bones (specimens 64, 65, 66). Of this pebbly limestone, or calcareous grit, there are four layers, separated one from another by several yards of strata, and varying in thickness from a few inches to about a foot. The mountains on the opposite side of the plain are apparently composed of the same strata as the Rhenosterberg; for, taking a commanding position on one of the dykes, one can distinctly count the strata in the mountains on either side ; and so uniform are they in colour and thickness, so alike in height, and equally horizontal in position, that the idea at once forces itself upon the mind that they must at one time have been continuous. At one spot on the side of the Rhenosterberg is a Kloof where the author found some fossils imbedded in the rock; and he often regretted when visiting the spot that the Kaffirs had left him nothing but a hammer and old chisel that were thrown into the waggon at starting, as with better tools he might have obtained many more specimens. Here he found the specimens 68, 69, which appear to be casts of stems of plants in sandstone. The first bones he here discovered were those of the skeleton, specimen No. 83 (a small Dieynodon). They were directly in the water-course, and only a small piece of one part was at first visible. By dint of hammering and chiseling each succeeding portion revealed itself to view. Unfortunately the skull was wanting. Underneath a large part of it there was a whitish scaly appearance on the rock, which might have been the remains of the covering that the animal had when alive. Many portions of the strata here were matted together with the stem-like fossils, such as specimens 70-75. Specimens 76 to 82 (nodular concretions)appear to have been washed from the same strata.

British Fossils, Stratigraphically Arranged

The Llandovery rocks were so named by Sir R. Murchison from the locality in South Wales where they are most fully developed, and where their physical relations to the formations above and below them are clearly exposed. Those rocks constitute an intermediate place in the Silurian table, connecting, by some of their contained organic remains, the fauna of the upper and lower Silurian groups. The upper Llandovery rock contains many shells common to the Wenlock beds, and is considered to form the natural base of those deposits; on the other hand, the lower Llandovery is related by its fossils to the Caradoc beds below, and both members of this formation are united by having certain fossils in common and peculiar to them, but are chiefly characterized by the abundance of some species of Petraia, Atrypa, and especially Pentamerus. This group consists of soft, argillaceous sandstones and building stones (Goleugoed), shales, some calcareous bands, hard, coarse grits, and quartzose, pebbly conglomerates. Thickness 2,000 to 3,000 feet.Localities.—Both members of this group, and their relations to the overlying and subjacent rocks, are well exhibited at Noeth Grüg, near Llandovery, South Wales. In Radnorshire, Shropshire, and Hereford, the upper member, or Pentamerus oblongus zone, is alone present, and is seen in some places to be unconformable to the Longmynd and Caradoc rocks. The conglomerates of the west flank of the Malverns, and the sandstones of May Hill and Huntly, Gloucestershire, are of this age.

On Yedmandale, as illustrating the Excavation of some Valleys in the Eastern Part of Yorkshire

T he Tabular Hills of the Eastern Moorlands of Yorkshire in their eastern part, that now under consideration, are very flat-topped, gradually rising from the vale of Pickering, on the south, where the elevation above the sea is about 100 feet, and attaining a height of about 600 feet at the escarpment six miles north of this, overlooking Harewood dale. The surface rock of the southern part is coralline oolite, which, however, has been removed from the northern part, where the calcareous grit is laid bare. Numerous ravine-like valleys, whose sides are inclined at an angle of about 30°, have been excavated in them, chiefly trending N.N.W.; but some are at right angles to that direction, being respectively nearly in the lines of the dip and strike of the beds, which, on the whole, lie nearly parallel to the surface. Many of these have been much modified by the streams now running in them, and present such appearances as might lead one at first to conclude that they had been altogether excavated by their action; and, indeed, there is nothing in their structure to prove decidedly that such was or was not the case. The peculiarity of Yedmandale, however, is, that there appears never to have been any brook or stream of modern drainage in its upper eastern branch, and that it is now in very nearly the same state as when first it emerged from those conditions of submersion which denuded the district. It is situated about four miles west

On the “Caradoc Sandstone” of Shropshire

Summary The conclusions to be drawn from the foregoing data may be thus shortly stated. The rocks east of the Longmynd hitherto known as Caradoc sandstone are now divided into two groups. The lowest and greatest portion is equivalent to the middle and upper portions of the Llandeilo and Bala rocks, and were accumulated in the following order:— 1. Fine shales, with small Trilobites ( Olenus, Asaphus, Agnostus ) and shells, deposited in deep water (most probably the equivalents of the Black Shales, Malvern). Elevation of Land, or Shallowing of Sea. 2. Coarse calcareous grits and conglomerate; a littoral or shallow water deposit. 3,4. Sandstones, with occasional pebbles, laminated in the upper parts, and in some localities northwards with many beds of shale. finer deposit than the last, and indicating a greater depth of water. Fossils exactly those of Bala. 5. Thin-bedded arenaceous shales, with fewer fossils, but of the same species; Trinucleus concentricus very abundant. A still greater depth of water is here indicated. (The higher part of the Llandeilo or Bala series.) Evidence of upheaval and partial dislocation. 6. A coarse deposit (unconformable on Nos. 1 to 5) in the immediate neighbourhood of the Longmynds, and derived from them (in part deep water around steep land, Forbes ). A great change in the organic remains. The characteristic Llandeilo and Bala fossils have given place to a mixed series, including several species found in the Upper Llandeilo flags, but with many others more characteristic of the Wenlock limestone. 7. Finer sandstones, with much shale and great abundance of Pentameri , and other Brachiopoda. Land gradually sinking ( Ramsay , Geol. Journ. vol. ix. p. 175). Fossils chiefly Upper Silurian. 8, 9. Grey and greenish shales, very fine sediment: deep water. Trilobites, Graptolites, and Cephalopods abundant. Fossils all Upper Silurian.