The theory of the gradual formation of overfolds and overfaults in a stratified system is thus developed by Professor Heim:—

Wherever a stratified rock series is subjected to the lateral horizontal thrust of the earth’s crust, a fold is originated. This fold consists of two opposed and symmetrical members, with more or less remote axes, viz. (Plate VIII. Fig. 1)

At the conclusion of my last paper on the Cheviot andesites and porphyrites (Geol. Mag. Vol. X. p. 262), I called attention to the close resemblance between the Cheviot hypersthene andesite (or porphyrite) and a rock from Steinerne Mann, Nahe, which has been called a proterobase. Both rocks are black in colour and consist macroscopically of glassy felspars (Mikrolin) imbedded in a groundmass which has a resinous or semi-resinous lustre. Microscopically they consist of two generations of felspar, pyroxene mostly rhombic, magnetite, and a glassy base with various devitrification products.

The Carboniferous Limestone of the north-west of England was formed in a bay separated from another marine area farther south by a narrow isthmus and promontory never submerged, extending, as Professor Jukes pointed out, in “a band of country running east and west across England from Leicestershire, through Warwickshire, South Staffordshire, North Shropshire into Montgomeryshire,” and to the mountainous district of North Wales.

In a previous paper of this series I endeavoured to show that the so-called Marine Drifts found at high levels, on both sides of the Irish Sea and elsewhere, are proved by their testaceous contents to have had no connection with the Glacial Age; while the mode of their distribution shows that ice in no form can have distributed them as we find them, nor yet are they consistent with the sub-mergence of the land for any considerable time beneath the sea; and I concluded that the only power known to us capable of distributing them is a wide-spread flood of water. I now propose to carry my argument considerably further, but before doing so, as it is so easy to be misunderstood, I must guard myself against the supposition that in what I have said or mean to say I am minimizing the Great Glacial Age.

The specimens selected for illustration of the shell-structure of this species of Chonetes were found in a bed of shale in the Lower Carboniferous Limestone series at Capelrig old quarry, in the parish of East Kilbride, Lanarkshire. The fossils in this shale have their structure generally well preserved, there being less change, through crystallization of the lime present in the shells of the various organisms, than is found in those obtained from most of the other fossiliferous localities in Western Scotland.

At page 37 of his chapter “On the Minute Structure of the Shells of the Brachiopoda,” and forming part of my work “On British Fossil Brachiopoda,” Dr. Carpenter says:— “Chonetes.— Of this genus, also, I have examined two species, armata and lata, both of which are perforated,”—but Dr. Carpenter does not explain in what way they are perforated, viz. whether these perforations pass through the entire thickness of the valve, or are restricted to a small portion of its thickness as in Productus.