GEOLOGY coals have originated from the growth of forests in situ, and were buried by beds of sand when the delta or coal jungle subsided and its surface was covered by water. The succession of coal seams through a great thickness of deposits points to a prolonged and extensive subsidence, marked by pauses sufficiently long for the silting up of the lagoons and jungles. But while we have proof that these coal seams were formed in situ, we have evidence likewise that some of the coal was formed by the drifting of vegetation into lakes by rivers and floods. The conditions of soil and climate must have been favourable to the growth of the prodigious masses of vegetation which, whether swept out to sea by floods or accumulated in forests and jungles, became submerged and were finally compressed and mineralized into our seams of coal. PERMIAN The Coal Measures are overlain unconformably by a series of lime- stones, sandstones and marls which belong to the Permian series. The name Permian was given to these rocks because of their wide develop- ment in the Russian province of Perm. Compared with the Carboniferous the Permian rocks are comparatively barren of life. Their fauna contains an admixture of carboniferous types with others which are more akin to those of the Mesozoic which succeeded them. The general character of the Permian rocks and their impoverished fauna have been considered as evidence that they were formed in isolated basins or inland salt lakes in which the water underwent evaporation until chemical precipitation took place. In Derbyshire the Permian formation covers no large extent of the surface. It is found only in a narrow strip running north and south near the eastern boundary of the county. The high ground which it occupies forms a well defined escarpment resting on the Coal Measures below. This escarpment and the lower lying land of the Coal Measures are well seen between Chesterfield and Bolsover, and form a well known feature in the landscape. The Permian rocks of Derbyshire consist mainly of the Lower Magnesian Limestones and Sandstones, the Upper Magnesian Limestone being absent. In some places underneath the Magnesian Limestones there are present beds of coarse sandstone and conglomerate with marls and thin bands of limestone, and sometimes coarser beds containing frag- ments of sandstone and water-worn fragments of Mountain Limestone. Their maximum thickness is about 15 feet. It is difficult to estimate the thickness of the Magnesian Limestone owing to the false bedding which occurs in it, and the variations in character which take place at short distances render it impossible to correlate the beds. Near Bolsover it is supposed to be from 100 to 200 feet thick, but further south near Eastwood to be only about 30 feet. It has been largely quarried at Bolsover, Langwith, Stoney Haughton and Pleasley. It varies lithologically from a crystalline i 25 4
