1845.] Diluvial and Wave Translation Theories. 243 



or aqueous deposition, which are often reversed in the boulder gravels 

 and the heaviest fragments found uppermost ; 3rdly, the great rarity 

 of fossils. A few marine shells of an arctic character and the remains 

 of a mammoth have been found in the till of Ayrshire ; arctic marine 

 shells in that of North America ; and I have observed marine shells 

 of recent species in that of Cheshire. 



The boulder formation, in short, consists of usually unstratified 

 accumulations of clay, loam, silt, sand or gravel, often 100 feet thick, 

 imbedding sometimes great fragments of rock several yards in diame- 

 ter, torn in many instances from rocks, hundreds of miles distant, 

 separated by vallies, rivers, and even seas, as is the case in the drift 

 on the east coast of England, which imbeds granite blocks from the 

 mountains of Scandinavia. These deposits are sometimes capped by 

 stratified layers of sand and gravel, and occasionally contain marks 

 of stratification themselves. 



The observer having, by these marks, ascertained that he has a 

 boulder deposit before him, should note its general shape, direction 

 and dimensions. If it occurs in detached truncated mounds, or 

 tumuli like the terminal moraine of a glacier ? or like lateral moraines, 

 in longitudinal ridges with a double talus ? the continuity and pa- 

 rallelism at the same height which is supposed to distinguish the 

 lateral moraine of a glacier, from the debris disposed along the bottoms 

 of the vallies by currents ? The thickness and extent of the gravel, 

 sand, clay or loam composing the deposit, should also be noted ; the 

 nature of the beds it rests upon, and also of those above it; of all 

 which specimens should be sent, as well as of the curious pebbles, 

 sands, clays, &c. of the boulder deposit. It also should be noted whether 

 the stratified portions of the boulder clays or gravels be bent up or 

 contorted, as if by lateral pressure ; and whether the subjacent beds 

 have been conformably or similarly disturbed. 



The relative proportions of the pebbles of various sorts of rocks com- 

 posing the gravel, their relative size, degree of attrition or roundness, 

 should be ascertained ; and the different sites whence originally wash- 

 ed, searched for in the vicinity. 



The gravel, clays, mud and loam should be examined for fossils ; 

 and the condition of the latter, whether broken, water-worn or 

 entire, and in good preservation, noted. 



2 M 



