50 FOURTH REPORT — 1834. 



hundred shells from the eocene of Alabama, the right of priority 

 to the discovery of many of which, however, Mr. Conrad and he 

 dispute. 



Many scattered descriptions of parts of our tertiary field have 

 appeared from time to time in our Journals ; but as they have 

 contained little or no scientific geology, I do not deem it neces- 

 sary here to mention them. 



Cretaceous Formatio7is. — The survey just given of our ter- 

 tiary formations is calculated, I think, to show how greatly 

 formations of the same or nearly the same period, occurring in 

 remote regions, may differ both in mineralogical characters and 

 in organic remains. The peculiarities which distinguish the 

 tertiary rocks of this country from those of Europe are clearly 

 traceable to the general dissimilarity in the physical structure 

 of the two continents, particularl)^ in the almost total absence 

 of volcanic formations in the United States. 



This country, for a long series of periods, seems to have suf- 

 fered less repeated and powerful convulsions than the opposite 

 shores of Europe ; so that the same comparative exemption 

 from disturbances is as apparent in om- secondary as I have al- 

 ready shown it to be in our tertiary periods. I have already 

 noticed the remarkably small number of species of fossils com- 

 mon to the tertiaries of the two continents, and I doubt if we 

 shall ultimately establish any closer identity in those of the 

 group now before us. While the cretaceous formations of Eu- 

 rope, from Ireland to Russia, are characterized throughout by 

 a numerous class of peculiar fossils, it is not a little singular that 

 so few of the same species should present themselves in the 

 rocks of the corresponding period in America — not more than 

 two perhaps of the 108 which are known. This fact, in con- 

 junction with the no less striking one that we have yet disco- 

 vered no true chalk in North America, has made me hesitate to 

 apply without some qualification the received European names 

 to these formations. For our information regarding this groiip, 

 which embraces at present, perhaps, the most advanced portion 

 of our geology, we are mainly indebted to the writings and re- 

 searches of Dr. Samuel G. Morton, a new edition of whose work 

 having just appeared, I am enabled to present this branch of the 

 subject in its most complete state. 



Dr. Morton entitles these newest of our secondary beds the 

 * cretaceous gi'oup', and regards them as divisible into two forma- 

 tions, the lowest of which he calls the ferruginous sand, and the 

 upper the calcareous strata. A very few years ago the group in 

 question was not known to extend beyond the peninsula of New 

 Jersey and a small part of Delaware. Subsequent discoveries. 



