Revieivs — Delesse's Lithologie du Fond des Mers. 79 



lime whicb. is specially secreted by the molluscs peopling their 

 waters. On the other hand, the mud ejected by salses is not mixed 

 with debris of molluscs, and the carbonic acid by which it is ac- 

 companied can, besides, easily dissolve the carbonate of lime con- 

 tained by it. It will easily be perceived, then, that when a bed of 

 pure clay is met with intercalated between fossiliferous beds, there 

 is some probability that it has been ejected from the interior of the 

 earth, either by mud volcanos, or by any other eruptive phenomenon. 

 It is noteworthy, moreover, that clay-beds being impervious to 

 subterranean waters, they could not completely lose their car- 

 bonate of lime by solution ; therefore, when they do not contain any 

 now, it is pretty certain that they had none originally. 



Let us observe, besides, that the muddy ejectamenta must, like all 

 eruptive phenomena, have been more frequent during the geological 

 periods preceding the present one. 



"III. Dislocations. 



The terrestrial crust is still subject to accidental dislocations, 

 occasioned by earthquakes, by eruptive phenomena, and, at rare 

 intervals, by the rising and sinking which accompany the upheaval 

 of mountain systems. 



The basin which contains the ocean is liable, then, to destruction 

 analogous to that to be observed on land. This destruction is pro- 

 duced at once by the forces acting in the interior of the earth, and 

 by the sea itself, which is suddenly put into motion. This being so, 

 the debris derived from, the bed of the ocean, and those which are 

 redistributed by the agitation of the waters, must concur to form 

 marine deposits. 



If one considers earthquakes, for instance, they are felt very 

 sensibly by ships, and the sea can transmit them enormous distances. 



When the earth's crust is alternately rising and sinking, its oscil- 

 lations engender forced waves, or waves of translation, which have 

 a great power, and which can -attain an exceptional height. At the 

 time of the earthquake at Concepcion, in Chile, it was specially 

 noted that the wave thus put in motion was propagated as far as the 

 Hawaii Islands, a distance of more than 683 miles. 



In France earthquakes are tolerably frequent; they are felt espe- 

 cially in the Gulf of Gascony and in the Mediterranean : but they 

 have not much influence on the formation of the marine deposits of 

 our coasts. 



If we go back to previous eras, when the mountain-chains 

 suddenly rose from the bottom of the sea, they certainly accumu- 

 lated an immense quantity of debris ; they also threw back 

 towards the surface subterranean waters charged with mud, which, 

 spreading over the submerged as well as the emerged land, deposited 

 thick beds of clay ; at the same time they gave birth to waves of 

 such power and height as it is difficult to realize. 



Without leaving French territory, the dislocations which gave to 

 the Pyrenees and to the Alps their principal relief suddenW brought 

 into play tremendous masses of water, by the side of which our 

 highest waves are, so to speak, of no account. They formed thick 



