46 Cretaceous. 



Teredo tibialis, now Polarthrus tibialis, Terebratula harlani, var. dis- 

 coidea, T. harlani, var. rectilatera, T. lachryma, now Terebratulina 

 lachryma, Pholas cithara, now Martesia. cithara, Balamis peregrinus, 

 Cidarites diatretum,now Cidaris diatretam, Clt/peaster Jlorealis, G. 

 geometricus^ and Spatangns ungula. Some of the species which he 

 described at this time, and refen-ed to the Cretaceous, are now regarded 

 as of Eocene age. Among these we may mention, NummKlites 

 manteUi, which has been the subject of much discussion, and is now 

 referred to D'Orbigny's genus Orbitoides, and chissed witli the Pro- 

 tista. 



In 1834, his Sj^nopsis appeared, illustrated with nineteen plates, and 

 having an appendix, containing a tabular view of the Tertiary fossils 

 hitherto discovered in North America. He said that he cast it, as " a 

 grain of sand, on the mountain of geological knowledge, which has 

 been heaped up by the genius and industry of the naturalists of both 

 hemispheres." But the carefulness with which the work was prepared, 

 and the sound discrimination and learning displayed upon every page, 

 are so obvious that one is struck with astonishment, in comparing it 

 with the peurile and hypothetical essaj's which emanated, at that time, 

 from the colleges and professed teachers of geology. It was not only 

 a valuable contribution to knowledge, prepared by a physician, during 

 the constant interruptions of a professional life, but it was the best 

 work which had appeared, at that time, upon American Geology, and 

 one that will continue to be a standard of science for many decades to 

 come. 



He separated the Cretaceous into two parts, the lower. Ferruginous 

 Sand, and the upper. Calcareous Strata. The mineralogical characters 

 of the Ferruginous Sand are extremely variable, consisting, for the 

 most part, however, of minute grains, collected into friable masses of a 

 bluish or greenish or grayish color, the predominant constituents of 

 which are silex and iron. Iron pyrites is found in profusion; succinite, 

 lignite and spheroidal masses, of a dark green color, and compact, sandy 

 structure are not uncommon. The calcareous strata consist of several 

 varieties of carbonate of lime, the principal of which are as follows: 

 an extremely friable mass, containing silex and iron, and about 

 37 per cent, of lime, composed almost entirely of disintegrated 

 zoophytes ; a yellowish or straw-colored limestone, full of organic 

 remains ; a granular or subcrystalline limestone, intermediate in 

 structure between the former two; and a white, soft limestone, not 

 harder than some coarse chalks and replete with fossils. All these va- 

 rieties are occasionally'^ infiltrated by silicious matter, and contain 



