• DRIFT MIXED UP WITH THE DETRITUS OF THE SPOT. 273 



degree of order to be evolved out of this apparent confusion ? Are the 

 general indications of agricultural geology (Lecture xi., §8, ) still, in any 

 degree, to be relied upon ? 



They are, and for the following, among other reasons : 



1°. It is stWl generally true that where a considerable extent of coun- 

 try rests upon any known rock, th6 soil in that district derives its usual 

 character from the nature of that rock. Thus though large portions of 

 Cheshire and Lancashire are covered with drift, yet the soil of these 

 counties, taken as a whole, has the general characters of the soils of 

 ihe new-red sand-stone, which in that part of England is so largely de- 

 veloped. 



2°. Where the drift overspreads any large area, it is found to become 

 gradually mixed up with the fragments, large and small, of the rocks 

 upon which it reposes. Thus in the neighbourhood of Durham, the 

 round hills of sand and gravel with intermingled coal consist in great 

 part of the ruins of the sand-stones of the country itself — while the 

 clays, no doubt, are partly derived from the shale beds which occur in- 

 termingled with the sand-stones of tl^ same coal measures. Hence the 

 soils of the northern half of this county, in general, still partake of the 

 usual qualities of those of the coal measures and mill-stone grit (pp. 

 249 and 250). In the western and higher part of the district they lie 

 more immediately on the rocks from which they have been derived, 

 while on the eastern half they rest on a mixture of the accumulated 

 ruins of the same rocks, which have been transported by natural agents 

 to a greater or less distance from their natural site. 



It is true that there are mixed up with these many portions of other 

 rocks brought from a still greater distance, but these bear but a small 

 proportion to the entire mass, and hence have, generally speaking, but 

 little influence in altering the mineral character of the whole. 



3°. It may indeed be staled as generally true, that the greater propor- 

 tion of the transported materials which lie upon any spot has been 

 brought only a comparatively small distance. Thus the sands and gra- 

 vels in the county of Durham — to the west of the magnesian lime- 

 stone — consist chiefly of the fragments of the coal measures. East and 

 south of the magnesian lime-stone escarpment (diagram, p. 271), they 

 become mixed with rounded masses of this lime-stone. On the new- 

 red sand -stone of the south-east of the county, they consist chiefly of 

 magnesian lime-stone mixed with fragments of the red sand-stone— 

 and on crossing the Tees, the debris of the lias hills begins to appear 

 among them. 



In countries, therefore, where drifted sands and gravels prevail on the 

 surface, they generally consist of the fragments of rocks which lie at no 

 great distance — generally towards the higher ground — the natural ten- 

 dency being for the debris of one kind of rock, or of one formation, to 

 overlap to a greater or less extent the surface of the adjoining rock or 

 formation. By this overlapping, the geographical position of a given 

 soil is removed to a greater or less distance beyond the line indicated by 

 'the geological position of the rocks from which it is derived. Thus, a 

 coal measure soil may overspread part of the rhagnesian lime-stone — 

 a red sand-stone soil may partially cover tiie lias, and so on — the general 



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