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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 20, 



not identical, then under what circumstances and within what limits 

 they are different. The received opinion is, that the majority of soils 

 have been formed in situ by the atmospheric erosion of the subjacent 

 strata ; and that the colours of Geological Maps as at present con- 

 structed may be received as exponents of the variations of soil. 



The study of the superficial deposits for more than twenty years, 

 several of which have been devoted to the mapping of the surface- 

 variations, has convinced me that this opinion is erroneous, and that 

 the majority of soils and subsoils in the British Isles are composed 

 only in part of the debris of the rocks on which they rest, and in part 

 of materials transported from various distances by forces of consi- 

 derable intensity, differing from ordinary atmospheric action, which 

 were in operation at the close of the glacial period. I have called 

 their results the Warp of the Drift, or the Erratic Warp. The 

 name is, perhaps, not the best that might have been selected ; but, 

 having adopted it in the first paper which I published on this subject, 

 I adhere to it until geologists shall substitute a better, or shall dis- 

 prove the existence of the deposit to which I apply the name. The 

 erratic warp answers to the "active soil" of agriculturists, which com- 

 prehends more than that portion of the soil actually cultivated. The 

 terminology of Agriculture is, however, too indefinite even for its own 

 purposes ; and it is not desirable to transfer it to Geology. 



During the examination of the superficial deposits, the results of 

 which are given in the communication immediately preceding this, 

 and in certain published and unpublished memoirs therein referred to, , 

 phsenomena were observed (p. 25) which afford at least strong pre- 

 sumptive evidence that the accumulation of many of those fluviatile 

 and lacustrine deposits which contain bones of large pachyderms, now 

 either wholly or locally extinct, associated with molluscs of nearly 

 the same species as those now inhabiting the neighbourhood, took 

 place after the emergence of Britain from beneath the glacial sea, 

 and prior to those aquatic operations, whatever they were, which 

 produced the erratic warp or surface-soil. If these views are correct, 

 it follows, that since the same mammals inhabited this country before 

 the glacial submergence and after it, and since the molluscs were in 

 both cases nearly the same, organic remains will afford little aid in 

 distinguishing deposits formed during different portions of one zoolo- 

 gical epoch. In these investigations, therefore, we must rely chiefly 

 on physical evidence, — on superposition when it can be found, and 

 on the relation of insulated deposits to other deposits whose date 

 can be ascertained by their superposition to strata of known age. 



If, for instance, we find that the beds of the Norwich Crag had been 

 converted into a terrestrial surface, inhabited conjointly by Rhinoceros 

 tichorhinusy Cuv. and R. leptorhinus* Cuv., and that the freshwater 

 deposits containing their remains are covered by the marine deposits 



* " Mr. Fitch of Norwich possesses specimens of upper and lower molar teeth 

 of the Rhinoceros leptorhinus from the freshwater (lignite) beds on the Norfolk 

 coast, near Cromer, which demonstrate the occurrence of this species in the same 

 deposit with R. tichorhinusy (Owen's Brit. Fossil Mammals, p. 381.) 



