236 MANUAL OF AGPJCULTURE, 



In the Carboniferous era, the soils of the coal measures groups 

 are inferior, and generally much neglected ; those of the mill- 

 stone grit are also poor and thin. In the mountain limestone 

 group, they are classed as of medium quality ; and, as in Derby- 

 shire, they afford good pasture ground. In the Permian, the 

 soils are of a light, dry description, and easily cultivable. As the 

 name implies, most of its limestone holds too much magnesia for 

 agricultural purposes. Of the Triassic era, the soils are variable. 

 They are kept under pasturage, over the marls, and are then good 

 for dairy purposes. Above the sandstones they are deep and 

 dry, although not of high quality. In the Jurassic, they range from 

 the densest quality, such as, e.g., Lias, Oxford, and Bradford stiff 

 clays, to that of a thin light sandy type. Excepting those above the 

 chalk marls, the gaults and wealden clays, the Cretaceous affords 

 soils of a light dry nature, which produce, under pasturage, an 

 excellent herbage, sweet and nutritious, and w^ell adapted for 

 sheep stock. Coming to the Eocene era, we find such dense soils 

 as the London clay, v/ith others of a lighter description in imme- 

 diate contact with them. In the Pliocene, we encounter the soils 

 typified by the rich alluvium of river-side deposits — the " carse", 

 lands of Scotland, deltas ; and also meet fens, peat-mosses, and 

 land reclaimed Dutch- wise, from the sea. 



In districts where the subsoil is deep, and a considerable space 

 intervenes between the upper soil and its underlying rocks, there 

 is generally a scarcity of stones for building or road-making pur- 

 poses ; and this is especially the case in clayey formations, and 

 those of the Pleistocene era. The clay, however, can be burnt 

 into bricks, and material in substitution of road "metal " — which 

 latter, however, is a poor make-shift for stone. The nature of the 

 subjacent rocky formations too has considerable influence upon the 

 question of water supply. Thus the numerous fissures in the 

 chalk and oolite formations act as natural main drains through- 

 out large areas, intensifying the droughts of hot summers. The 

 opposite extreme is reached when rocks or subsoils are of a close 

 or retentive description, unfavourable to the percolation of water. 

 Hence it is that a knowledge of the position and nature of the 

 subsoil and underlying rocks is essential in the conduct of exten- 

 sive drainage works. The term *'dip''" means the inclination of 

 strata to the earth's centre, and is measured by the angle formed 

 by the intersection of the pkme of the horizon with the plane of 

 the beds themselves. " Strike " means a line at right angles to 

 the dip. "Outcrop" is where the beds appear at the surface. By 

 rock " structure" is meant the peculiar arrangement of its com- 

 ponent x^arts in the mass, e.g., stratified or columnar structure 

 (^like that of the igneous rocks of Staffa and the Giant's Cause 

 w-ay.) "Texture" implies the minute arrangement of the com- 

 posing particles; and "compositions" applies to their chemical 



