On the Agricultural Geology of England and Wales. 457 



rock on which they rest, would produce considerable variations 

 from the standard assigned to the soils of each formation. 



On the other hand, variations in the strata, which have no exist- 

 ence, are assumed in explanation of variations of soil, which are 

 dependent on the superficial deposits. The doctrine, moreover^ 

 that the alluvium of each river or district varies with the geological 

 formations through which the rivers flow, can only be, admitted 

 as true of deposits of rivers flowing entirely through one or two 

 formations, which are very rare instances except in the case of 

 the minor tributaries. A glance at a geological map is sufficient 

 to show that the Thames, the Severn, and the rivers which flow 

 into the estuaries of the Wash and the H umber, unwater catch- 

 ment basins, composed of many formations, and covered by 

 erratic tertiaries of considerable thickness which contain a great 

 variety of fragmentary matter derived from diff"erent quarters. 

 The fine detritus of such rivers which reaches their mouths and 

 enters into the composition of the soils of our principal alluvial 

 districts must therefore be of a very mixed character. Professor 

 Phillips has shown, moreover, that the warp deposited by the 

 H umber is derived more from the wasting cliffs of Holderness, 

 brought up with the tide, than from detritus brougl^t down from 

 the interior by the rivers ; and recent microscopic researches have 

 established the fact that a large proportion is not detritus of any 

 kind, but made up of the siliceous covering of minute animal- 

 cules. 



It is, however, needless to insist on these poinis, as we have 

 reason to believe that Mr. Morton's views have undergone con- 

 siderable modification, and that he now finds warp of the drift," 

 and " basins of drift," in many situations where he would formerly 

 have considered the soil to be derived exclusively from the subja- 

 cent rock. His work has the merit of having once more drawn 

 attention to the subject of agricultural geology, which had long 

 been dormant, and of being a good first approximation to results 

 which require for their completion much more extended observa- 

 tion than they have yet received. An examination of the soils of 

 England and Wales for the purpose of determining their varia - 

 tions and their relation to the rock formations of our geological 

 maps, or to the erratic tertiaries which are excluded from them, 

 would require the constant work of ten surveyors for thirty 

 years. 



Professor Johnston, in his Lectures on Agricultural Chemistry 

 and Geology, has acknowledged his obligations to Mr. Morton 

 for the description of the agricultural characters of the strata of 

 the south of England. Residing, however, in the north, in a dis- 

 trict thickly covered with erratic tertiaries or drift, he has been 

 more impressed with their influence on the distribution of soils. 



