EXTENSION OF THE ANTI[,LEAN CONTINENT. IZo 



Turiunu- to the land features, it a.])|)ear8 that tlie more or less upturned 

 Pliocene beds were being extensively eroded into broad valleys, with the 

 fjords creeping inland. Even the little valley of the Yuniuri of Cuba 

 was excavated to a widtli of three miles, and the same is true of several 

 valleys in Jamaica, San Domingo and Costa Rica, which are exca- 

 vated out of Pliocene limestones and other strata* The valley of Atrato, 

 in Coloml)ia, which is 40 or 50 miles wide, is more recent than the 

 Miocene period. The elevated valleys, with bases 1,500 feet above the 

 sea, in the Trinidad mountains of Cuba, and similar valleys in Jamaica, 

 up to 3,000 feet, have been elevated much more recently than even the 

 Pliocene erosion which molded their forms to a great extent. Such 

 valleys are being now produced b}^ widening of the rai)idl3'' growing 

 canyons. In short, at that time the Antillean mountains were not rela- 

 tively so high above sealevel as now. The Pliocene drainage reduced 

 the valleys to the lowest level, and these were miles in width. It was 

 then that the modern topography was first well established. The dura- 

 tion of the epoch of erosion was long, and the formations which were 

 degraded were those that formed the surface of the country which was 

 largely covered by ^Miocene deposits. Thus the Matanzas fjord was first 

 entirely excavated to a depth of 1,500 feet before joining the outer fjord. 

 The Pliocene deposits of southern Florida occupy a broad, shallow basin, 

 with the older Miocene formations rising on both sides.* In short, 

 throughout most of the Pliocene period the continental elevation con- 

 tinued with the degradation of the surface into canyons extending far 

 inland, but not so far as to carve deep valley's into the interior of the 

 then elevated tablelands which now constitute the coastal plains, except 

 such as are now buried to the depth of a few hundred feet. 



The geologic development of Central America is yet somewhat hyjio- 

 thetical. That the drainage was toward the Pacific is highly proba])le' 

 if not certain, since the characteristics of the adjacent portions of the 

 ocean bed indicate a continuation of the Gulf and Cari])bean valleys and 

 ])lains; but in the great oscillations of the land from abyssmal depths to 

 continental elevations of 8,000 or 12,000 feet some insular masses doubt- 

 less rose into j)rominence. Such heights would refer mostly to the region 

 of the (Ireater Antilles and the adjacent continents, for the Gulf and 

 Caril)l)ean plains must have Ijeen low. The former tablelands are in 

 part illustrated ])y the modern great plateau l)asin of Mexico and the 

 tal)lelands of Guatamala, whicli rise from 0,500 to 8,000 feet al)()ve the 

 sea, or by the still higher tablelands of Asia. 



During tlie Pliocene elevation there was at least one volcano in 

 Jamaica,"}" and some of the volcanoes of Central America appear to liave 



♦ Bull. U. S. Geol. Surv,, no. 81, ♦' Neocene Correlation Paper," by W. H. Dall, map, page 166. 

 t Geology of Jamaica, p. 120. 



