﻿152 GEOLOGICAL ACTION OF 



the alluvial deposits of the Gulf of Lyons. Thus the matter deposited by the currents 

 of the tides, acting in conformity with the principles here laid down, has become by sub- 

 sequent upheaval the means of uniting the former island, but now peninsula, of Spain to 

 the continent of Europe. This is an instance of bay deposit. 



Another instance of bay deposit is the great tertiary basin of Paris, confined on the 

 lower sides and to the west by the Jurassic and cretaceous regions, and separated in part 

 from the tertiary of Belgium by the upper chalk. 



A third striking case of the bay deposit in the tertiary period is the clay basin of 

 London, the limits of which are determined by the upper secondary, bounding it on all 

 sides except at the entrance. The tertiary of Hampshire is a case of sound deposit, and 

 that of Norfolk and Suffolk occurs (as has been said of the alluvium lying outside of it) 

 precisely at the region of meeting of the tides coming from the Straits of Dover and the 

 North Sea, where a convergence and retardation of the tide-waves creates the circum- 

 stances under which the sea parts easily with the matter held in suspension. 



All the previous cases have been cited merely as examples. Having before me the 

 magnificent geological maps of France, and the maps of other parts of Europe, it would 

 be very easy to multiply the number of them ; but these are sufficient for illustration. 



An interesting application of this theory is suggested by Mr. Desor, as follows. 

 Geologists have observed that there occur in the same geological horizon deposits differ- 

 ing entirely in mineralogical character and in fossil remains. Gressly, who with careful* 

 accuracy traced out the line of demarcation between such deposits in his Observations 

 sur le Jura Soleurois,* and fully recognized their peculiarities, gave them a distinct classi- 

 fication, in which he included the muddy region (fades vaseux) and the shoal region 

 (fades de charriage). If, adds Mr. Desor, the upheaval of this continent should affect 

 the south coast of Massachusetts so as to expose the bottom of Cape Cod Bay or of 

 Nantucket Sound, there would be seen in those places precisely the same varieties of 

 formation and condition as in the tertiary of the Swiss valley. These geological pecu- 

 liarities, then, are accounted for when we consider the latter as the sound and bay de- 

 posits of the tertiary period, and, this view being correct, it will be a future demand 

 upon the attention of the geologist to endeavour to identify in similar cases all those 

 varieties of form and conditions of deposit which are typified in the alluvial and sub- 

 aqueous deposits of the actual epoch. 



Professor A. Gray has called my attention to the manner in which this theory may 

 be made to throw light upon the geographical distribution of certain plants. The dune 



* Memoirs of the Helvetic Society of Science. 



