202 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



cording to A. Agassiz,^ this is mostly of a Pacific type, which has existed 

 in the Gulf and Caribbean since at least as far back as Cretaceous time. 

 The minority of Atlantic forms from this fauna may also suggest that a 

 partial barrier at least then existed to the eastward, side of the Carib- 

 bean. From Florida to the northeast corner of South America we now 

 have a chain of submerged banks, which constitute the rim of the Gulf 

 and Caribbean basins and which may or may not represent elements of 

 this ancient Jura-Cretaceous Isthmus, — the same which has been fre- 

 quently used as data for constructing a hypothetical and impossible 

 Windward bridge during later epochs. This is still covered by coatingi 

 of oceanic debris, or capped by volcanic ejecta, which rise at intervals as 

 tips of land above it. The configuration of these submerged rims and 

 islands is that of an old dissected land. 



The submerged bench off the Floridian coast deflects southeastward 

 towards and practically continuous with that of the Bahaman banks, 

 where its continuity is broken by great western indentations extending 

 along the north side of Eastern Cuba, Haiti, Porto Rico, and the Virgin 

 Islands. Thence along the Windvard Archipelago to the South American 

 coast there are many banks which might be construed as such elements. 

 The present outer rim of the American Mediterranean may indicate the 

 former continuity of the Isthmian region of Jurassic time. If the Wind- 

 ward bridge did not exist at this period, it never existed, — certainly not 

 since Eocene time, as will be shown later. 



Hovey has described a series of specimens obtained from a well bored 

 to a depth of 2,000 feet at Key West.^ The Yicksburg formation was 

 penetrated completely, the boring passing into the underlying Eocene 

 between the depths of 1,450 and 1,875 feet. It is quite probable that 

 the former is the base of the Vicksburg. There is indisputable geologic 

 evidence in the land-derived material of the Eocene sedimentary rocks 

 of the Antilles, the Virgin Islands, the Caribbees, and Barbados, that land 

 areas from which they were derived existed in this general region in 

 Cretaceous time. 



Westward of this hypothetical bridge there could have stood but one 

 or possibly two islets in the present Central American region south of 

 the southern end of the Mexican Cordilleras. Rising east and west 

 tiirough the States of Oaxaca, Chiapas, and Guatemala, and probably 

 in Cuba and Haiti, there are ancient ridges of Paleozoic sediments and 

 igneous rocks, — short crescents curving to the northward and now 



1 Three Cruises of the Blake, Vol. I. p. 1G7. 



2 Bull. Mus. Comp. ZoOl., 1896, Vol. XXVIII. No. 3. 



