592 POPULAR SCIENCE MONTHLY. 



physical testimony of the recent great changes which have occurred 

 in the Central American and West Indian regions. 



On the Confirmation of the West Indian Continent by Cen- 

 tral American Phenomena. — The Reconstruction of the Antillean 

 Continent,* and The West Indian Bridge between ISTorth and South 

 America, -f- have been largely based upon the testimony of the great 

 river channels being traceable as drowned valleys of natural pro- 

 portions across the submerged plateaus or margins of the land to 

 the floors of the Gulf and Caribbean basins, which are characterized 

 by large plains. This fundamental feature is supported by a great 

 array of facts collected by the writer and described in the papers 

 named. It was during the early part of the Pleistocene period that 

 the West Indies were united into a high plateau and the floors of 

 the sea basins were transformed into plains, to the margins of which 

 the river valleys have been traced. The continuance of the river 

 valleys to the floors of the sea basins is the result of their formation 

 upon the surface of the land before the region was submerged be- 

 neath the oceanic waters. Satisfactory as was the evidence of the 

 high continental elevation to the east, the Central American region 

 now appears as a barrier against its former drainage to the Pacific, 

 thus producing inclosed sea basins. On a smaller scale, there is a 

 perfect analogy in the basin of Lake Ontario, which is only the 

 valley of the St. Lawrence, mostly closed by warping of the earth's 

 crust so as to raise up a barrier of several hundred feet in place 

 of thousands of feet, as is the case in Central America. It was very 

 significant that the depressions in the Mexican and Central American 

 table-lands correspond only to the extensions of the West Indian 

 basins, thus suggesting the location of their outlet. But the dis- 

 covery of the recent general elevation of the American barrier to 

 thousands of feet, and the preservation of the last water ways across 

 the divide, are found to show that the barrier did not obtain at the 

 time when the Antillean basins, according to the hypothesis, should 

 have been drained into the Pacific. Thus the low altitude of Cen- 

 tral America at the time of the high continental elevation to the 

 east and the presence of the recent water ways to the Pacific Ocean, 

 lately discovered, complete, in a manner, the story of the great oscil- 

 lations of land and sea in the regions between ISTorth and South 

 America. 



Of the two miles or two miles and a half in height of the Central 

 American barrier above the fioor of the sea basins, probably half that 

 amount has been produced by gentle warping of the earth's crust, 

 ximounting to only a few feet per mile, like that across the outlet 



* Bulletin of the Geological Society of America, vol. vi, pp. 103-140, 1894. 

 •)• Appletons' Popular Science Monthly, vol. liii, pp. 10-30, 1898. 



