GO THE PRINCIPLES OF 



is known as the London clay; and where these beds occur 

 we find the very reverse of what might be expected. An 

 intimate knowledge of surface as well as of block geology is 

 needed before a conclusion as to the relation between the 

 nature of the surface soil and the characteristics of particular 

 formations can be arrived at. 



Similarly we might make a serious error if we concluded 

 that all the soils upon the lias clay are stiff. The occurrence 

 of sand beds in the lias clay often modifies the soil, and 

 explains the presence of light land even in valleys of the lias. 

 Neither must the student forget the overspreading of a great 

 part of the North and Midlands of England with drifted 

 materials, sometimes many feet in thickness, which have 

 overspread the main geological formations, and given the 

 surface a fresh character. Take, for instance, the new red 

 sandstone, which, as a rule, yields a red soil of high 

 average fertility. That character of the new red sandstone 

 is well maintained in Warwickshire, Worcestershire, Derby- 

 shire, Cheshire, Cumberland, and in Yorkshire. But when 

 we cross the Tees into the county of Durham, although upon 

 the geological map the peculiar colouring of the new red 

 sandstone predominates, the soil alters in character to a poor 

 boulder clay of considerable depth. That boulder clay, or 

 drift clay, masks the character of the new red sandstone. 

 No longer does the new red sandstone actually form the 

 surface, but a cold, intractable, and infertile soil, which 

 spreads over a great portion of the south-east of Durham, 

 and not only masks and covers the new red sandstone, but 

 likewise to a great extent the magnesian limestone adjoining. 

 Accidental features may also be introduced by the occurrence 

 of peat, which may be found upon any geological formation, 

 as, for example, where the Oxford clay is largely covered with 

 peat in East Anglia, and again where, south of Doncaster, 

 and in the neighbourhood of Selby, the new red sandstone 



