The compact limestone of England and Wales be longs properly to the transition rocks. In Yorkshire and the northern counties it rests on slate, and con tains a greater quantity of organic remains than the De vonshire limestone. Trap, or greenstone, is met with in Cornwall in transition rocks ; but it possesses no cha racters by which it can be distinguished from that found in primary rocks.
Transitions from granite to sienite and greenstone occur in the same block at Charnwood Forest. The two latter are also met with in Cornwall, Wales, and Cumberland. Amygdaloid, provincially called toad stone, is found in great abundance in Derbyshire. Porphyry occurs in the western side of England and Wales. It has already been mentioned, that porphy ritic greenstone is scattered over the northern side of Cader Idris. Basalt is found in Durham, Shropshire, &c.
The lowest of the secondary rocks in England is frequently a silicious sandstone, coloured by red oxide of iron, and called red sandstone: this has been already described. The secondary rocks also include argilla ceous sandstone, earthy limestone, calcareous sand stone, and chalk ; and contain, besides the rock-salt, gypsum, iron-stone, coal, and basalt. On the eastern side of England, the coal strata generally decline to the south-east ; on the western side, they are more fre quently thrown into different and opposite directions, by faults and dikes. The deepest coal mines in Eng land are those of Northumberland and Durham, some of which are wrought more than 300 yards below the surface. The thickest bed of English coal is in Staf fordshire, which is 30 feet deep. In general, the beds of coal in other parts of England and Wales do not ex ceed from 6 to 9 feet in thickness. From the account which we have already given of the low district of Eng land, it will be apparent, that there is more than one third of this country, in which all search for valuable coal is useless.
Witt respect to the upper secondary rocks, and the strata containing organic remains in England, there are magnesian limestone, chalk, flint, gypsum, the mark and sand over which, in many parts, contain a large quantity of red oxide of iron. Gypsum is principally found in Cheshire, Shropshire, Worcestershire, Derby shire, and Nottinghamshire, In the gypsum of the two latter counties, no organic remains have been dis covered. The organic remains found in the clay and gravel which covers the chalk in the southern counties, have already been noticed. The gravel over the clay
is composed principally of flint, containing distinct im pressions of unknown aquatic animals. Between the clay and the gravel, there is sometimes a thin layer of fresh-water shells, which are also met with under the clay. In the strata over chalk, in the isle of 'Wight, fresh-water shells have lately been detected.
If we were to cross England, from Hull into Lanca shire, we should first meet with a flat country, formed of alluvial ground. A few miles to the west of this town, the land becomes more elevated, and we pass over a range of chalk hills, which compose the southern extremity of the Yorkshire Wolds. After descending from these hills, near the Humber, we again enter on alluvial ground, covered with clay and gravel, which extends nearly to Ferrybridge. Here the magnesian limestone makes its appearance, which, with the earthy limestone, form hills of a low elevation, distinctly stra tified. The strata are nearly horizontal, and divided by seams of clay. The extreme breadth of this range of hills is not more than three miles. Yellow siliciouc sandstone comes next, which is the boundary of the low calcareous district. Proceeding towards Wakefield, the argillaceous coal strata of the middle district, ex tending westward more than 20 miles, is met with Wakefield and Leeds stand near the cast side of the coal district, and Huddersfield and Halifax near the western. A few miles to the west of these towns, and also of Sheffield, hills, composed of millstone grit and shale grit, rise from under the coal strata. These arc more than 300 yards thick, and no workable coal is ever found in them. The bases of these hills is metal liferous limestone. If we proceed still farther to the west toward Manchester, we descend the steep west ern declivities to the plains of Lancashire ; and, leav ing the millstone grit and shale grit, we again come upon coal strata, which, still farther to the west, are cut off, or partially intercepted by the red silicious sand stone already described. The surface here in many parts is covered by beds of gravel ; and in clay pits, under the surface, are found detached blocks of gra nite, basalt, sienite, and slate, similar to the rocks in North Wales and Westmoreland. From the vicinity of Prescot to Liverpool, the immediate substratum is form ed by the red rocks, which may be seen dipping under the waves of the Irish Sea.