Such are the imperfect outlines of the general physical conditions which are represented by the series of sedimentary strata included in the Carboniferous system. At the close of this period, the Earth’s surface in Western Europe was subjected to crust-foldings on a large scale, along lines running approximately North and South and East and West, the two sets of movements resulting in the formation of ridges of Carboniferous rocks. The uppermost series of grits, sandstones and coal-seams were in great part removed by denudation from the crests of the elevated ridges, but remained in the intervening troughs or basins where they were less exposed to denudation. It is the direct consequence of this, that we have our Coal-Measures preserved in the form of detached basins of upper Carboniferous beds. A closer examination of the comparative thickness and succession of Carboniferous rocks in different parts of Britain shows very clearly that in the northern area of Scotland and in the North of England the conditions were different from those which obtained further South. Seeing how much palaeobotanical interest attaches to these rocks, it is important to treat a little more fully of their geology. In parts of Devon, Cornwall and West Somerset, the Devonian strata are succeeded by a series of folded and contorted rocks which have yielded a comparatively small number of Carboniferous fossils. To this succession of limestones, shales and grits the term _Culm-Measures_ was applied by Sedgwick and Murchison in 1837. The rocks of this series occupy a trough between the Devonian rocks of North and South Devon. While some authorities have correlated the Culm-Measures with the Millstone Grit, others regard them as representing a portion of the true Coal-Measures, as well as the Carboniferous and Lower Limestone Shale[55]. It has recently been shown that among the lower Culm strata there occur bands of ancient deep-sea sediments, consisting of beds of chert containing siliceous casts of various species of Radiolaria. There can be no doubt that the discovery of deep-sea fossils in this particular development of the British Carboniferous system leads to the conclusion that “while the massive deposits of the Carboniferous limestone—formed of the skeletons of calcareous organisms—were in process of growth in the seas to the North, there existed to the South-west a deeper ocean in which siliceous organisms predominated and formed these siliceous radiolarian rocks[56].” The Upper Culm-Measures consist of conglomerates, grits, sandstones and shales with some plant remains and other fossils, and constitute a typical set of shallow water sediments. In Westphalia, the Harz region, Thuringia, Silesia and Moravia there are rocks corresponding to the Culm-Measures of Devon, and some of these have also afforded evidence of deep water conditions. [Sidenote: COAL-MEASURES.]