CHAPTER I. 



INTEODUCTORY. 



The existence of a series of deposits and accumulations, inter- 

 vening between the vegetable soil and the older strata of the 

 earth's crust, has long been known to Geologists ; they rest in- 

 discriminately on formations of Tertiary, Secondary or Primary 

 age, and they form what farmers call the sub-soil over large 

 portions of those districts in the British Islands which have 

 been brought under cultivation. Notwithstanding, however, 

 their importance from an agricultural point of view, these 

 superficial deposits were little studied in the early days of 

 Geology, and the first endeavours to account for their occur- 

 rence were very crude and unsatisfactory ; it is only indeed 

 within the last 20 or 25 years that they have received that 

 amount of attention which they merited, and only within the 

 last 10 or 12 that Geologists have been able to give anything 

 like an adequate and comprehensive account of their distri- 

 bution and mode of formation. 



By the Huttonians these deposits were all classed together, 

 and regarded as the result of atmospheric action and fluviatile 

 erosion on the surface of the continents during a long lapse of 

 ages. The possibility of separating them into two groups or 

 series, differing in their constitution and mode of occurrence, 

 was first indicated by Cuvier in the Preface to his work on 

 "Fossil Quadrupeds" at the close of the last century (1798), 

 In this preliminary essay, now known under the name of 

 " Cuvier's Theory of the Earth," (which was translated into 

 English in 1813) he speaks of the beds forming the Paris basin 

 as surmounted by various alluvial rleposifs. He notices that some 



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