512 PBOCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 17, 



both is sufficient to prove their synchronism. But we are able still 

 further to extend the limits of this Miocene Sea. In the cutting for 

 the Panama Railway, shelly beds were passed through near Navy 

 Port, at a height of 15 feet above the sea, from which Mr. Saunders 

 collected some fossils which he presented to this Society. Most of 

 them are too imperfect for determination; but out of less than a 

 dozen, which are tolerably distinguishable, five are certainly identical 

 with San Domingan Shells : they are, Conus Doming ensis t a Malea, a 

 Natica, a Venus, and a Cardium *. 



In my Reports on the San-Domingan Shells t, I mentioned that one 

 or two seemed identical with Shells now living in the Pacific, and 

 that the nearest analogues of several others were to be found in the 

 Pacific, and not in the Atlantic Ocean : several striking instances of 

 these resemblances were mentioned. The collection now before us 

 also presents the same feature ; for although all the specimens I 

 have identified with recent Shells are now living in the West Indian 

 seas, yet the affinities of several others are decidedly with Shells of 

 the Pacific Ocean. I may mention a Venus belonging to a group 

 confined to Australia ; a Corbula scarcely distinguishable from C. 

 modesta, Philippine Islands ; a Pleurotoma very near, if not identical 

 with, P. nigerrima, Panama ; and another very close to P. gibbosa, 

 Cumana ; besides which, some of the San-Domingan Shells which 

 presented this character in a marked degree also occur in Jamaica. 

 Observing this in the San-Domingan collection, I formerly threw out 

 the conjecture that the separation between these seas may not have 

 been so complete in early Tertiary times as at present. Dr. Duncan's 

 Memoir, just quoted, throws great light on this question. It results 

 from his studies, that the relation between these fossil Corals and 

 those now living in the Pacific or China seas is even more intimate 

 than that indicated by the Mollusca. Some of these species are 

 actually now living in the Pacific, and others belong to genera of 

 which all the living species are confined to that ocean. 



M. d'Orbigny, in his great work, ' L'Amerique Meridionale,' 

 shows that five of the Cretaceous fossils from the western side of 

 South America are identical with five in the Paris Chalk, while of all 

 the Tertiary fossils on the two flanks of the Cordilleras not a single 

 one is common to both formations ; and he thence infers that a com- 

 munication must have subsisted between those two oceans during 

 the Cretaceous period, and that at its close the upheaving of the 

 Cordilleras effected that separation which has subsisted to this day. 

 But it is to be observed that the Tertiary fossils collected by M. 

 d'Orbigny were all found south of latitude 30° S., whereas those 

 from Jamaica and San Domingo are in latitude 18° N. Even if 

 some connexion had existed between the two oceans in the district 

 of Panama, as is now supposed, the Mollusca living on the two 

 flanks of South America, 40° to the south of that opening, might 

 be expected to be distinct, just as those at present living on the 



* See Quart. Journ. Geol. Soc. vol. ix. p. 132. 

 t Ibid. vol. vi. p. 40, and vol. ix. p. 129. 



