240 ME. JTJKES-BKOWNE AND PROF. HARRISON 



woiilcl also be submerged by a depression of 500 feet, and much of 

 Mexico near the isthmus of Tehuantepec ; for, according to the 

 data in Mr. Easton's possession, only about a mile of the watershed 

 in the pass of Tehuantepec rises above 500 feet. 



A submergence of 1000 feet would, therefore, cover some breadth 

 of the Tehuantepec isthmus, and would leave little of Panama and 

 Costa Rica above the sea ; Mcaragua would be broken up into a 

 group of islands, and parts of Honduras and Guatemala would form 

 larger islands rising from 2000 to 3000 feet above the waves. 



Now a thousand feet is only half the amount of the elevation 

 indicated by the raised reefs of the Antilles ; hence we reach the 

 important conclusion that, for a long period of time, no land con- 

 nexion existed between North and South America, Central America 

 then forming a group of islands which might be regarded as merely 

 a western part of the Caribbean Archipelago. In connexion with 

 this supposition, it is interesting to note the fact that the fauna and 

 flora of the Greater Antilles (Cuba, Jamaica, &c.) have closer 

 affinities with those of Central America than with those of Florida 

 or of South America. 



The severance of North and South America at some epoch in 

 Tertiarj' time is by no means a new suggestion, but we believe 

 that this is the first occasion on which the idea has been discussed 

 in connexion with definite geological e\ddence, pointing to a com- 

 paratively recent date for the sundering of the two continents. 



The question has hitherto been obscured by the supposed Miocene 

 date of so many of the West-Indian deposits, and even Prof. Alex. 

 Agassiz, in his most recent publication ('■'■ The Three Cruises of 

 the ' Elake ' "), seems to have missed seeing the possibility of such 

 recent communication between the Pacific and Atlantic Oceans. 

 In his fifth chai)ter he specially discusses the relation of the 

 American and West-Indian faunas, and indicates the connexion 

 which would have existed on the assumption that at some previous 

 period the whole region stood 3000 feet higher than it does now. 

 He does not give any geological evidence for this supposition, but 

 merely speculates upon the geographical conditions which would 

 exist if at any previous period the 500-fathom line formed a coast- 

 line. The idea was, in fact, suggested by the hydrographical sur- 

 vey of the region carried on by the " Blake " Expeditions, and we 

 should not have referred to it had he not strangely included the 

 possibility of a communication with the Pacific in his hypothetical 

 restoration. 



After showing that such an elevation would unite Plorida to 

 Cuba, and leave only very narrow passages at certain points along 

 the Antillean chain, he says : — " At the time of this connection, if 

 it existed, the Caribbean Sea was connected with the Atlantic only 

 by " (certain passages mentioned) . . . *' The Caribbean Sea, there- 

 fore, must have been a gulf of the Pacific, or have been connected 

 with it by wide passages, of which we find the traces in the Ter- 

 tiary and Cretaceous deposits of the Isthmus of Darien, of Panama, 

 and of Nicaragua." 



