387 



deposition of the Upper Lias. Turning from these physical 

 considerations to the fossil evidence, Mr. Day mentions a 

 singular fact as to the restricted range of the Ammonites, 

 and particularly in respect to the Zone in question. "Ammonites 

 margaritatus, Montf. appears with the sand and mica in the 

 "Three Tiers," (See Generalized Section of the Middle and 

 Upper Lias of the Dorsetshire Coast, p. 288,) and disappears 

 again with a deposit of marl ; its place is, however, on the 

 recurrence of sand, supplied by a closely allied form — Am. 

 Spinatus, Brtjg." Again, he observes that " In the lower part 

 of the "Spinatus Zone " there appears to be a different fauna 

 from that of the sands below, and in its upper portion occurs 

 the most remarkable collection of Mollusca of any in the Lias." 

 An inspection of M. Delesse's magnificent "Carte Lithologique 

 des Mers de France," clearly demonstrates to us the nature of 

 the hydrographic basin, the petrology of the channel lying 

 . between the English and French coasts, and other striking 

 phenomena ; but the facts deduced for our purpose lie out before 

 the eye more vividly, that is, the prolongation of the strata 

 connected throughout so as to bridge the Channel geologically, 

 and thus effect a continuity with the North West of France, and 

 particularly with the Calvados. The French series of Liassic 

 deposits in the North West were laid down under such strange 

 and exceptional conditions that a true sequence cannot be 

 expected. These conditions I have touched on elsewhere, and 

 will not enlarge on.* The numerous works of the younger M. J. 

 EuDES Deslongchamps on the Lias of the Calvados district 

 should be consulted, as to the details of the Liassic strata 

 lying deposed between and upon ridges of old rocks of schistous 

 and metamorphosed structure. It is plain that even in this 

 abnormal condition of the deposits, some succession of beds is 

 possible, for M. J. Etjdes Deslongchamps fils, in his last com- 

 munication with me, mentioned their Spinatus Zone. 



For Normandy, Department of the Calvados and Lower Seine, 

 we submit the follomng succession from the MM. Deslongchamps 

 in their brochure entitled "Memoire sur la couche a Leptgeria du 



*See Paper "On the occurrence of Plicatula lajvigata, &;c.." in the Proc. 

 Cotteswold Club, 1876. 



