Having given this general description of the of England, we shall now proceed to a more particular account of it, as well as of its mineral geography.
What has been denominated the low district of Eng land, is distinguished, as has been already remarked, by the absence of any regular bads of coal or metallic veins. Chalk, roe-stone, calcareous sandstone, and earthy lime stone, principally compose it. Earthy limestone and calcareous sandstone, extend from Dorchester to Nor thamptonshire, and on the eastern side of Leicestershire, Nottinghamshire, and Yorkshire, into part of Durham and Northumberland. The eat thy limestone in this dis trict is far from being pure : it is gell'•rally of a yellow colour, and some of it contains 20 per cent. of magnesia. In the magnesia)) limestone, there are few organic re mains. The strata lie very nearly horizontal, and arc, in almost every situation, very distinctly seen. Mag nesia» lime, however, occurs in this district, composed of beds that are singularly contorted and much elevated. Between the chalk and the limestone, different kinds of calcareous sandstone occur ; the most singular and im portant, is the oolite or roc-stone, of which the Portland stone, and the Kctton stone of Northamptonshire are varieties. The roe-stone is separated from the chalk by beds of sand and sandstone mixed with clay these ex tend with a considerable degree of regularity over the whole of the south-east of England, but vary much in their thickness. It has, however, been remarked, that in the midland and northern counties, less regularity can be distinguished, and that many of the strata, which are distinctly seen in the south, are there entirely missing. Above the chalk, in the low district, lie, in gencral,"thick beds of clay and gravel. In the upper part of this clay, the hones of the elk, the hippopotamus, and the elephant, have been found. In the southern counties, from Dor setshire to Kent, and in the midland and eastern counties of Wiltshire, Berkshire, Hertfordshire, Buckingham shire, Essex, Cambridge, Norfolk, Lincoln, and the east riding of Yorkshire, chalk makes its appearance, in dif ferent situations, from under the clay. As the general
rise of the strata is to the north, as w e approach the coal districts, the strata, which lie under the chalk, rise to the surface. The depth and succession of the strata between the chalk and the coal, have not been ascertained with any degree of minuteness and accuracy, except in one or two places. Mr Townshend, in a work entitled, cc The character of Moses vindicated as an Historian," has given the following as the thickness and succession of the strata from the chalk on the south coast to the coal districts of Somcrsetshirc. Soil and alluvial ground, various thickness ; chalk more than 400 feet ; three beds of green, grey, and red sand, with sandstone, noo feet ; clay 200 feet ; superior oolite, or roe-stone, 40 feet ; cal careous grit, 30 feet ; coral rag, 30 feet ; forest marble, 40 feet ; great oolite, or Bathstone, 140 feet ; clay, 140 feet ; inferior oolite and sand, 80 feet ; blue clay, 70 feet; lyas, 60 feet ; and red marle, 130 feet. Hence it is pro bable, that, allowing for the depth of the stratum of clay over chalk, the depth of the strata in that part of the low district of England, which comprehends the vale of the Thames, to the strata containing coals, will amount to about 700 yards ; but if we estimate the depth of the ar gillaceous strata, containing coal, where the chalk ter minates, and the subjacent sand rises from under it, as at Woburn in Bedfordshire, it probably will not amount to more than 350 yards.
It has been already remarked, that the mineral pro ducts of this district are few and trilling : iron pyrites is met with crystallized in some parts of the chalk rocks, and crystals of sulphate of barytes, have lately been dis covered in the pits of fuller's earth near Reegatc in Surry. Fuller's earth, also, is peculiar to the strata under chalk. The iron-stone, which is found in part of this district, is not so rich as to bear the expellee of bringing fuel from a distance to smelt it. The bones of quadrupeds, already mentioned, are never found in the strata below the chalk, but always in the clay over the chalk.