290 Organic Remains of the 



whole that Dr. Morton's inference seems in a great measure estab- 

 lished. How far the cretaceous group of the United States may be 

 separated beneath and above, from other deposits more or less con- 

 temporaneous with those of Europe, remains an interesting problem 

 which it is hoped American geologists will endeavor to solve. — As- 

 suming that the American ferruginous sand formation belongs to this 

 [cretaceous] group, of which there seems great probability, it would 

 appear that the great white carbonate of lime deposit, or chalk, did 

 not extend there ; but that a series of sands, clays and gravels con- 

 stituted the whole group." 



In reference to the preceding passages, I may briefly observe, that 

 the whole super-cretaceous group, or tertiary series, (excepting only 

 the fresh water deposits) is now satisfactorily identified in this coun- 

 try. Thus we have the upper, middle and lower tertiary forma- 

 tions,* all based directly or indirectly on the ferruginous sand j and 

 I may repeat, that so far as my observations have extended, not a 

 solitary fossil of the latter formation has been detected in the super- 

 posed strata. 



In resuming the subject of organic remains it may be observed, 

 that I have figured on the present occasion, some of the most re- 

 markable species only, the remaining illustrations being reserved for 

 a separate edition of this Synopsis : for the same reason the plates 

 here given do not follow each other in numerical order. 



ORGANIC REMAINS. 

 CHAMBERED UNIVALVES. 



AMMONITES. 



A. telifer. (S. G. M.) A remarkable species, of which I possess 

 several fragments from the Delaware marl, almost too imperfect for 

 description, and yet so different from the other species as to induce 

 me to give it a name. It will be figured^ in the second edition of 

 this Synopsis. 



I take this occasion to remark that the A. hippocrepis of DeKay, 

 inserted in the first part of this Synopsis, is merely a transverse section 

 of ScapMtes Cvvieri. This formation, therefore, possesses but four 

 published species of Ammonites, viz. A. placenta, A. Delawarensis, 

 A' Vanuxemi and A. telifer. 



* I take the liberty (for reasons to be given in another place) of substituting these 

 names for those of Upper marine, London clay and Plastic clay formations. 



