348 



THE GEOLOGIST. 



which alone I shall occupy myself at present, (as it alone con- 

 tains Ammonites), the seas of this period changed their form. 

 The two basins of Paris and Provence, of which I have 

 spoken, existed in their full integrity, but the latter had con- 

 siderably enlarged, extending as far as Cotentin on the one 

 side, and over the whole Gulf of the Loire, until that time 

 devoid of the cretaceous formation ; whilst the basin of the 

 Pyrenees, one of the largest of that period, also received 

 throughout its whole extent, the seas of the epoch of the 

 coloritic chalk. Thus, in the third group of the cretaceous 

 rocks, there existed three distinct basins, those of Provence, 

 Paris, and the Pyrenees, containing distinct species ; but 

 these basins had undoubtedly more communication with each 

 other than at an earher period, and therefore furnish a larger 

 number of species common to all, intermingled with those 

 pecuhar to each. 



The effect of the denudations which occurred at the pe- 

 riod of the Gault were still in action at the time of the depo- 

 sit of the first beds of the chloritic chalk, since, as I have 

 before remarked, we find at certain places where the Gault 

 has disappeared, as at Havre and Cassis, a mixture of fossils 

 evidently transported, some of which belong to the Gault and 

 others to the chloritic chalk, the enveloping mass only 

 containing, as I satisfied myself, the foraminifers of the pe- 

 riod of the chloritic chalk, which proves that these deposits 

 belong to that group, and that the species of the Gault have 

 been transported thither. The upper portions appear to 

 have been deposited in a more regular manner, especially in 

 the basin of the Pyrenees and in the Gulf of the Loire, where 

 none of these mixtures exist, except in the lower beds.- 



The Ammonites found in all the basins are the following : 

 A Rhotomagensis, A, Mantellii, and A. varians. 



