Feet Of Shale Research Articles

Amphitheater Valley Heads

In an article recently published in the Journal of Geology, Freeman' described the topographic characters and mode of origin of certain valley heads in an anticlinal mountain range in central Montana; these valley heads, because of their similarity to glacial cirques, were called pseudo-cirques. The series of rocks present in the range consists of 2,300 feet of limestone, underlain, in order of position, by 700 feet of shale, 80-100 feet of quartzite conglomerate, and 200 feet of shale. Since no evidences of glaciation have been observed anywhere in the range, the origin of the amphitheater-like valley heads was ascribed to the undermining of the relatively easily eroded shales, and the continuous steepening of the resistant limestone faces by the collapse of unsupported masses of that rock. Freeman considered that certain structural conditions are specially favorable for the production of these great amphitheater valley heads: (i) an anticlinal fold with nearly flat, thick, resistant strata at the top or along the axis of the anticline, and steeply dipping strata along the limbs; (2) a sufficient area of flat-lying beds to permit the development of the amphitheaters; and (3) soft, easily eroded strata underlying the resistant beds. In regions of flat-lying or gently dipping strata, composed of thick, resistant members underlain by thinner beds of weak rocks, the development of amphitheater valley heads takes place if the streams have cut through a resistant layer into the weaker rocks below. The perfection of form and the size of the amphitheaters depend upon various conditions. Of prime importance are the thickness, the number, and the resistance of the harder strata. If more than one thick, resistant bed, separated by weaker layers, be

The Barrettia Beds of Jamaica

Barrettia, the most abnormal of the Rudistæ, and among the strangest of all the mollusca, was first found in Jamaica by Lucas Barrett, F.G.S., in the year 1861. The specimens were ably described by S. P. Woodward, F.G.S., in 1862. The original specimens, now in the British Museum of Natural History, consist of polished transverse and longitudinal sections of the upper part of the shell, the latter showing the junction of the upper and lower valves, and a cross section of the young shell near the apex of the lower valve. They were called Barrettia monilifera in honour of the discoverer. The locality where they were found was on the banks of the Back River, a tributary of the Rio Grande, about 15 miles from the coast in Portland Parish in the north-east of the island. The rock is described as a hard, grey limestone which occurs in bands of a few inches to a yard in thickness, subordinate to many hundreds of feet of shale which graduate up into other grey shales of the Eocene, followed by white limestones of Miocene age.

Note on the Well-Section at Rock Mills and the Fauna associated with Edestus

The well at Rock Mills (Messrs. Joseph Sykes & Co.) is situated in the mill-grounds in the valley of the River Hohne at Brockholes, about 4 miles south of Huddersfield. According to the Geologiqal Survey-map (Quarter-Sheet 88 S.E.), the alluvimn in the valley at this point rests on shales which underlie the Rough Rock, the uppermost member of the Millstone Grit. The shales appear to vary considerably in thickness in this district. Green states that 100 feet of shales are present between the Rough Rock and Grit A about Holmfirth, which lies 2 miles south of Brockholes; while on Holestone Moor, west of Huddersfield, he estimates that thev are 200 feet thick between the same horizons. Spencer has shown that in the district embraced in the next sheet to the north (Quarter-Sheet 88 N.E.) the shales contain a marine fauna; and the discovery of Edestus should stimulate the efforts of the local geologists to further work on this horizon. During the excavation of the well no record of the various strata passed through was made by the sinkers; but it appears, from notes supplied by Mr. J. R. Simpson, of Banks, Honley, that the rocks were mainly shales, with some thin beds of sandstone. At the depth of 120 feet the specimen of Edestus was obtained by Mr. H. H. Freer in a bed of rock—rather friable shale,—which also contained numerous fragments of marine shells. Among the specimens the following have been identified:— Posidoniella lœvis (Brown), Gastrioceras sp., Glyphioceras reticulatum (Phill.)

The Recurrence of Tropidoleptus Carinatus in the Chemung Fauna of Virginia

For many years after the standard sections of the New York Devonian formations and their faunas had become well known, the brachiopod Tropidoleptus carinatus was supposed to be confined in its geologic range to the I,Ioo or 1,200 feet of shale comprising the Hamilton formation in central New York. No trace of this fossil has ever been found in the typical Genesee and Portage faunas which follow the Hamilton fauna in west central New York. The entire absence of the species from the Genesee and western Portage faunas of New York seemed to indicate that the life of the species came to an end with the close of Hamilton sedimentation in central New York. But the discovery of T. carinatus in the Chemung of southern New York 2,000 feet above the top of the Hamilton by Professor H. S. Williams' several years ago proved that this species instead of becoming extinct at the close of the Hamilton had only changed its habitat. More recently Williams and Kindle3 have found that Tropidoleptus carinatus and other well-known Hamilton species comprise the major part of the fauna at certain Chemung horizons in southern New York 2,000 feet or more above the top of the Hamilton formation. In this paper it will be shown that this and other Hamilton species reappear in the Chemung fauna of Virginia as they do in New York. The appearance of T. carinatus in the Chemung fauna of Virginia in abundance is especially notable because it is seldom found at the horizon of the Hamilton fauna so far to the southwest in this part of the Allegheny region as the occurrence in the rocks of Chemung time which will be described.

Glacial Rock Sliding

A geological curiosity in the shape of a displaced mass of rock resulting from ice-pressure during the glacial invasion has been partially uncovered in the Voight quarry, three miles north of Elmira, N. Y., and one-half mile south of Latta Brook ravine. Reference may be had to the Elmira sheet of the United States Geological Survey, but the contour lines represent the topography only in a general way. The quarry is located in the face of a ledge which extends out some 300 feet from the main hill. At its southern end the cutting is only 37 feet deep, but the linear extent is nearly 400 feet. The bottom is about 35 feet above the valley level, making the present approximate height of the point 70 feet. Massive sandstones form the bottom of the quarry, but they rapidly thin out, and the upper third is very largely composed of shale. This formation has received the local name High Point sandstones.' The strata have a northward dip of about 50 feet per mile, and their position indicates that the axial inclination of the Elmira anticline, to which they belong, is fully as great eastward. Their position was, therefore, an important factor in the amount of pressure required to move the load. The south side of the ledge is in the form of steps or small terraces, which remain as they were in preglacial times, and it is down over this serrated slope that the rock mass was shoved. Its present form is indicated much more clearly by the accompanying sketch than it could be by a detailed description. The base or shoe on which the slide occurred is a hard, blocky sandstone 12 inches thick, and it is chiefly owing to this fact that its character can be recognized. Any attempt to delimit the slide must be largely conjectural, owing to the till covering. There are 50 feet of the basal sandstone in sight, and at one point 7 feet of shale and thin sandstones remain

The Rhætic and Lower Lias of Sedbury Cliff, near Chepstow (Monmouthshire)

On the opposite side of the Severn to Aust Cliff, and 2 miles north-north-west of that section, there is a corresponding elevation known as Beachley, Aunard9s, or Sedbury Cliff. Chepstow lies to the west-north-west, and in a direct line is distant about miles, but by road about miles. I have distinguished the cliff-section as that of Sedbury, since Sedbury Park, the country-seat of Sir William Marling, Bart.—to whom, and to Mr. S. S. Marling, I am indebted for permission to examine the cliff and for kind assistance—is situated on the Rhætic and Liassic outlier. The literature relating to the section is not voluminous. In that which has come under my notice I find it incidentally mentioned in several papers,1 and briefly noticed in two other communications. The earliest account is that given by the Rev. P. B. Brodie, but it is based upon information supplied by Mr. Higgins. This account may be summarized as follows. There is a development of true ‘Insect-Limestone’ above the ‘Landscape-Stone,’ and although they are separated one from the other by 4 feet of shale at the eastern end of the section, at the western they thin out and blend as at Aust. The ‘Landscape-Stone’ contains a great variety of insect-remains, some of which are tolerably perfect. The ‘<i>Cypris</i>- and Plant-Bed’ is seen in its proper position, and in every case possesses a true ‘Landscape’ character. Sir W. V. Guise observed that this section closely resembled the exposure at Aust, yet presented differences which

IV.—On a New Marine Bed in the Lower Oolites of East Yorkshire

About half-way between Hayburn Wyke and Cloughton Wyke, and five miles North of Scarborough, a scar of hard sandstone, remarkable for its even bedding, may be seen rising with a considerable dip from the sea. This sandstone contains along its bedding planes occasional thin layers of a very dense ironstone, from which it has probably received the name of ”Iron Scar.“ Immediately beneath are about five feet of shales closely resembling those of the Middle Lias, and containing two bands of dogger ironstone.