Order Of Superposition Research Articles

On the Tertiary Strata and their Dislocations in the Neighbourhood of Blackheath

T he cuttings of the North Kent Railway yielded some good sections of the Plastic Clay series, and disclosed an important line of dislocation at Deptford;—important because a close approximation to its date can be obtained, and because it has affected the present configuration of the adjoining country. The abrupt escarpment of the chalk and plastic clay along the south side of the Thames is manifestly due in some measure to this dislocation, which also accounts for the presence of the London clay under the Greenwich marshes at an unexpectedly low level. Before proceeding to consider the effects of this dislocation, it will be well to describe the strata which it has affected. And this description derives interest from the fact that these strata are perfectly regular over a large extent of country; their order of superposition and organic contents being constant, and their mineral composition exhibiting no great variation. Table I. shows the localities where the succession of strata may be most advantageously studied; and Table II. the correspondence between the subdivisions existing in this district and those observed elsewhere, and recorded by Mr. Prestwich.*

Contributions to the Geology of North Wales

The author made a tour in North Wales, having two objects principally in view: the first, to classify the stratified rocks of that country; the second, to ascertain what are the beds that lie below the Silurian rocks of Sir R. Murchison, and whether those beds contain any organic remains. After first observing the structure of those parts of the country where the order of superposition in the beds was already known, he proceeded to examine other districts where the arrangement of the rocks is more obscure and complicated. Upper Silurian Rocks.—Llangollen district He began by studying the Llangollen district, described by the late Mr. Brown. He agrees that geologist in referring the Upper Silurian rocks in that neighbourhood, partly to the Ludlow and partly to the Wenlock series of Sir R. Murchison. Ludlow series. — This series, in descending order, consists of 1. Thin, grey, micaceous beds, containing Terebratula navicula, Leptæna lata, several species of Cypricardia, and other fossils 2. Liver-coloured shales. 3. Blue shale The distinction which exists in the English border countries, between the Upper and Lower Ludlow beds, cannot her be made out; nor is there any trace of the Aymestry limestrone. There are so few fossils in the greater part of the Ludlow amd Wenlock series in North Wales, that it is by differences of colour or minieral composition that one is often obliged to distinguish them. The Ludlow series is of soft texture, is

On the Tertiary or Supracretaceous Formations of the Isle of Wight as exhibited in the Sections at Alum Bay and White Cliff Bay

In the London tertiary district there are but few good sections of the middle and upper Eocene strata; and there is no part of it in which the order of superposition is so well shown, or can be so conveniently studied, as in the coast sections of Hampshire and of the Isle of Wight. Owing to this better and more permanent stratigraphical evidence, it may be desirable, before treating of the London tertiaries, to fix the subdivisions of the contemporaneous Hampshire series, in order that they may serve as types and points of reference. I therefore beg to submit to the Society the following observations made in the autumn of 1839, which I should have brought forward at an earlier period, had I not hoped to have rendered them more complete by a further examination of the district, which however I have not had leisure since to resume. The general details of this subject are well known. I will briefly note the results obtained by former observers, and then examine in succession the development and nature of the organic remains, conjointly with the changes of lithological characters and of dip, and I hope these may tend to remove some of the uncertainty and doubt which seem still to exist, particularly on the continent, on the subject of the fauna of these strata, and on the period of the disturbance by which they have been affected. Their age and synchronism with the Paris groups also require, I think, some material revision.

XXXIII.—On the Geology of Coalbrook Dale.

Illustrations.—Pl. XXXV. to XLI. Introduction. In the following pages two memoirs are embodied. One of them, read before the Society in February 1834, gave a short account of some of the principal faults and disturbances of the Coalbrook Dale coal-field; the other, read April 1836, described the several formations comprised in that district, as well as certain phænomena exhibited by the coal-measures, and not noticed in the former communication. Before I proceed, it is necessary to observe, that prior to the researches of Mr. Murchison into the formations between the carboniferous rocks and the slates of Wales, the examination, of the Coalbrook Dale district was attended with very considerable difficulties. A few of the rocks, which crop out against the flanks of the Wrekin, had been ascertained to be counterparts of others; but their order of superposition and relative antiquity had not been determined. Mr. Murchison’s labours, however, have removed these difficulties, by showing, that the thin zones of gray and liver-coloured sandstones, shales, and limestones, which overlie the limestone at Wenlock, and underlie the coal-measures at Madeley, Broseley, &c., are referable to the Ludlow rocks, the first formation beneath the old red sandstone, and constituting, with the Wenlock limestone and shale, the upper Silurian group; and that the shelly sandstone at Morrell’s Wood, as well as the quartzose grit, and dark-coloured flags at the base of the Wrekin, belong to the Caradoc sandstone, or lower Silurian rocks. The deposits just noticed form, in this district, the terminating points

XIX.—On the Freshwater Strata of Hordwell Cliff, Beacon Cliff, and Barton Cliff, Hampshire.

In the last volume of the Transactions of the Geological Society, there is a description of the strata in the cliffs between Lymington and Muddiford near Christchurch; and, in a section accompanying the Memoir, the extent of the different formations exhibited in this line of coast is laid down. Large collections of the fossils of these cliffs have been made since the days of Brander, who published an account of them in 1766; and many have paid hasty visits to the spot, for the purpose chiefly of procuring fossil shells. But it was reserved for Mr. Webster to discover and first make known, in 1822, the existence of a distinct freshwater formation on the Hampshire coast, corresponding with the lower freshwater formation in the Isle of Wight. I have examined these freshwater strata in minute detail, their order of superposition, and their organic contents, with a view of furnishing data to geologists, for comparing these beds with those of the opposite coast of the Isle of Wight; and also to decide the question, on which doubts were entertained by the author of the Memoir above mentioned, whether the upper marine formation occupies any portion of Hordwell Cliff. In determining the names of the shells, I am indebted to the kindness of Mr. James Sowerby; without whose assistance in examining specimens of the marls brought from these cliffs, several of the organic remains would have been entirely overlooked. The following is a list of the beds in the order of their