76 Revieivs — Delesse^s Lithologie du Fond des Mers. 



Ill, — Marine Deposits of the French Coasts. 



Littoral and submarine deposits. 



Distribution of Mollusca. 



IV. — Lithology of the principal Seas of the Glohe. 



France. — New World. — Old World. 



V. — France at different Geological Epochs. 



Deposits of the old French seas. 



Deformations undergone by these deposits. 

 It will be seen that under each of these heads can be grouped a 

 very considerable number of geological facts and problems, and the 

 author is not one likely to slur over his work. Indeed, he appears 

 to have not only collected all the available evidence as to the nature 

 of the bottoms at innumerable points of the ocean, but to have made 

 in person, or through his assistants, analyses of a large proportion 

 of the soundings obtained. As is natural in a national work, those 

 portions of it which are immediately connected with France are 

 treated in a much more exhaustive manner than those relating to 

 other parts of the world. It is partly for this reason that I know 

 that M. Delesse is anxious that English geologists should be made 

 acquainted with the less extensive but equally important pages of 

 his work which relate to the seas of Britain, and with the more 

 general results of his investigations, which must be of interest to 

 geologists of every country. My task, therefore, in the present 

 article is simply that of laying before the readers of the Geological 

 Magazine as fair an abstract as I am able of those points just re- 

 ferred to, giving the author's views without criticism or comment, 

 leaving such disquisitions for a future occasion. 



I. — -The methods employed in studying the deposits need not 

 detain us. They consist in ordinary chemical analysis, sifting and 

 washing. One point, however, is worth noting in passing. It is that 

 in the residue of washings, even of very argillaceous deposits, a great 

 abundance of silex, and especially of quartz,^ is invariably present. 

 This fact gives one a good idea of the complexity of origin of most 

 of the bottoms, and cannot fail to add greatly to the difficulty expe- 

 rienced in tracing them back to their parent rocks. 



II. — Among the organic agencies contributing to the formation of 

 marine deposits, M. Delesse numbers not only the enormous amount of 

 debris due to mollusca and marine vegetables, but also such a slow and 

 comparatively weak action as that of boring shells and echinoderms 

 in eroding the walls of the sea, and the cumulative action of corals 

 and other stationary organisms. " In the sea," he says, " vegetation 

 carries on a slow degradation of the sides. It must especially deeply 

 corrode calcareous rocks, as has been shown to be the case in the 

 Swiss lakes. In course of time, lacustrine or marine plants produce, 

 in short, destructive effects analogous to those of terrestrial plants." 



III. — These effects are, however, tolerably well understood, and it is 

 with regard to the inorganic agents that our author holds less gener- 

 ally received opinions. As far, indeed, as the ordinai-y sources of denu- 



' M. Delesse does not seem to have used polarized lig-ht in ascertaining the flinty 

 or quartzose origin of grains of sand. (See Nature, 9tli May, 1872.) 



