1862.] 43 



the debris in the various directions and distinct areas could have 

 been effected ; the one by the rise of the land from beneath the sea, 

 and the other by the action of rivers on a larger scale than the 

 present ones. As the later tertiary deposits show the existence of 

 seas or of lakes over the districts in question, it follows as a necessary 

 consequence that when the land rose from beneath them, a mass of 

 debris, in quantity and length of transport proportionate to the 

 greater or lesser rate of elevation, must have been spread over the 

 bottom of the channels along which the water flowed off. Nearly 

 associated with the high-level gravels there are remnants of another 

 drift which may have had this older and independent origin. This 

 mode of formation could not, however, be applied to the valley gravels, 

 as they contain freshwater shells such as live in rivers, with land 

 shells and mammalian remains, proving the existence of a dry land. 

 The author concludes that the high-level gravels are the result 

 of river-action which took place at a period before the excavation of 

 the present river-valleys. With regard to the mode of formation of 

 these gravels, he remarks on the materials being often transported 

 a considerable distance, the frequent presence of large blocks or 

 boulders of the harder rocks, the presence of a certain proportion 

 of angular debris, and the commonly confused bedding and con- 

 tortions. He shows this to exist in England and in France, and 

 supports the case by quotations from various French authors. It 

 is then shown that in the valley of the Somme these phenomena 

 are most marked and decisive, large blocks of sandstone, some 

 weighing four to five tons, and derived from tertiary strata twenty to 

 forty miles above Amiens, being found in the St. Acheul gravels, 

 and the beds being much contorted. These contortions do not depend 

 on any pressure exercised by the blocks, but result from some dis- 

 turbing power applied and removed. To illustrate this point refer- 

 ence is made to two sections in his former paper (Phil. Trans, for 

 I860, p. 299). 



The author conceives that the only adequate cause to produce many 

 of these effects is river-ice, the transporting power of which is well 

 known, whilst he quotes the observations of travellers in Northern 

 America to prove the power of such ice to pile-up the shore 

 shingle in great conical heaps. That the old pleistocene rivers were 

 also larger and more rapid than the existing rivers is evident from 



