344 



THE GEOLOGIST. 



A fact which I have noticed in all the localities of the 

 Gault, and which strengthens the hypothesis that at this pe- 

 riod of the cretaceous formation there have been numerous 

 dislocations, and therefore that many strata have disappeared 

 in certain quarters and interrupted the regular order of suc- 

 cession, is that the strata have almost always been disturbed 

 and abraded, either at the period of their deposit, or pos- 

 teriorly and at an epoch when their organic remains had be- 

 come in some measure fossilised. Were I to search for 

 examples of what I advance, I should find evidences of it : 

 1st. in the lower beds of Wissant; 2nd. in those of the 

 Ardennes and Meuse, where the fossils, enclosed in a very 

 compact black rock, have been thus rolled and deposited in 

 beds, in an argillaceous or siliceous deposit, which is evi- 

 dently posterior to the former ; 3rd. in the upper beds of 

 Gasty and Maurepaire (Aube), where nodules, still harder, 

 doubtless rolled in water, and inclosing A. Interruptus in the 

 adult state, and a number of other fossils are disposed in 

 beds in the midst of the upper argillaceous strata, containing 

 A. latidorsatus, which is never found in the nodules, and 

 which I have observed, is always found in the upper portions 

 of this division ; thus the nodules in these instances belong 

 to an epoch anterior to that of the argillaceous strata in 

 which they^are found. These facts, which all geologists may 

 observe as well as myself, easily explain why the Gault only 

 forms thin deposits in general, which we can follow around 

 the several basins, as we find in the case of the white chalk 

 of the Neocomien and likewise of the Jurassic formation. 

 This also proves that the period of the Gault has been marked 

 by extensive denudations ; that violent currents, which were 

 either general or produced by dislocations, have, throughout 

 almost all the strata of this period, prevented a gentle and 

 gradual deposit, tearing up the deposits at one place, to bear 

 them to another. 



