456 Action of the Atmosphere upon newly-deepened Soil. 



tlie southern half of Ireland and England, continuing it eastward 

 so as to strike against the Ural chain of Russia ; thus including 

 almost the whole of Central and Northern Europe. {Meyn. of 

 Geological Survey, i. 351.) Tliis elevated sea-bottom, then, now 

 presents itself in the form of great sheets of clay, gravel, sand, 

 inud, and loamy earth, either stratified or unstratified, with here 

 and there the subjacent rock peeping through. It varies greatly 

 in different localities both as to quality and thickness, and oc- 

 cupies all altitudes, from the sea-level up to 1400 or 1500 feet, 

 the clays and marls being generally inferior to the gravels. This 

 mass in any one locality is in general mainly derived from the 

 rocks in the quarter of the country where it is situated, but con- 

 tains often a multitude of miscellaneous materials which have 

 come frequently from a great distance, and that from a north 

 direction, or from points to the east or west of north. 1 hus, 

 above the chalk rocks it may be chiefly composed of the debris 

 of that formation ; over the old red sandstone, chiefly^ of ma- 

 terials of the Devonian kind ; over limestone mostly of calcareous 

 matter ; and, in the north of Scotland, in a great measure, of the 

 component parts of the primary and trap rocks. But although in 

 the south-eastern counties, such as Cambridge, Suffolk, Essex, 

 &c., there will be often many fragments whose source must be 

 looked for in the far north, amongst the hills perhaps of North- 

 umberland or Inverness, yet we never find materials from the 

 middle of England in the north ; never, for instance, boulders of 

 chalk in the till of Perthshire. 



Although in some places no foreign matter is to be met with, 

 yet we find this heterogeneous mixture extending south as far 

 as even the suburbs of London ; but beyond the metropolis, in 

 Surrey, Kent, Sussex, and other parts of the southern division of 

 the kingdom, the boulder clay is wanting ; and although super- 

 ficial deposits are to be met with in parts of even the southern- 

 most counties, yet they seem less general and of a different 

 character, and in many districts the soil seems to be derived 

 immediately from the subjacent rock. 



We have, therefore, in Britain tlie greater portion of the surface 

 occupied with this mixed deposit, and a comparatively small 

 area in the south wltliout it. This latter portion may have pro- 

 bably been in part land during the glacial epoch, and it is only 

 in it that we may with some greater degree of certainty expect to 

 find the arable soil characteristic of the rocks which lie imme- 

 diately below it. Fortunately part of this area has been explored 

 by tlie Geological Survey, and the results given to the public. 

 Accordingly, we find Sir Henry De la Beche, in speaking of the 

 surface of Cornwall, Devon, and West Somerset, say — " The 

 fertility of the district is found to var\' most materially, and, 

 taking the geological map in our hand, we ascertain that this 



