104 J. W. SPENCER — RECONSTRUCTION OP ANTILLEAN CONTINENT. 



lean lands would be extended if the region were uniformly raised 6,000 

 feet. The charts of Agassiz '^ and others show the positions of the sub- 

 merged basins. Geologists have demonstrated the great changes of level 

 to which the Caribbean region has been subjected, but I am not aware 

 that an}^ geologist has hitherto f attempted to restore the topography of 

 the submerged continent and set forth the geomorphic evidence that the 

 drowned valleys are those of former lands, now depressed beneath the 

 sea. The later changes of level have had far reaching effects, not only 

 on the geographic forms, but on the climate of, perhaps, the whole At- 

 lantic basin. These changes have also placed obstacles in the way of the 

 distribution and development of life, or cut off and exterminated such 

 forms as reached the Antillean lands, and have given rise to the modern 

 distribution of Atlantic and Pacific types in the waters of the West 

 Indies. 



The present contribution is primarily based on the physical geology of 

 the Antillean region. The phenomena of first importance are the fjords, 

 revealed by the now numerous soundings, in connection with the land 

 valleys of the continents and islands. Some of the valleys are now 

 wholly submerged, even to their sources. The formation of the valleys 

 at various elevations, depending on baselevel of erosion ; the continua- 

 tion, of the valleys into fjords; the deformation of deserted water-mar- 

 gins by warping or terrestrial undulations, as recorded in the elevated 

 terraces, beaches and other shore phenomena ; the successive cycles of 

 erosion and filling of the valleys, with the consequent unconformity of 

 the strata, and the distribution and elevation of the later formations, with 

 the subsequent erosion — all of these phenomena are made use of in the 

 study set forth in this paper. Some difficulties yet remain, but to geo- 

 morphy we ma}^ hopefully look for their removal. The dynamic studies 

 explain many biologic phenomena, and these in turn support the con- 

 clusions regarding the physical history of the continent. 



This investigation is the sequence to years of inquiry into the geologic 

 history of the Great lakes. Their depth indicates a former elevation of 

 the continent considerably above the present altitude In looking for 

 proofs of this greater altitude it was found that the fjords of the coast in 

 higher latitudes are only submerged valleys. J At that time the writer 

 hesitated to admit continental changes of level greater than 3,000 feet, 

 but Avith increasing knowledge of deep submerged valleys elsewhere, no- 

 tably the much deeper fjords of the Antillean region, and with the find- 



* "Three Cruises of the Blake," by A. Agassiz, vol. 1, 1888, figs. 56 and 57. 



t An adyanced notice of some of the drowned valleys appeared in Bull. Geol Soc. Am., vol. v, 1893, 

 p. 10, under the title of "Terrestrial Submergence Southeast of the American Continent," by the 

 writer. 



J "High Continental Elevation preceding the Pleistocene Period," by J. W. Spencer, Bull. Geol. 

 Soc. Am., vol. 1, 1889, p. 65. 



