88 J. W. SPENCER — GEOGRAPHICAL EVOLUTION OF CUBA. 



bay there are four lower terraces inscribed upon the rocks. The one at 

 about 25 feet above tide is the most strongly marked. 



From the character of the erosion of the terraces it is pro])able that all 

 of the terraces except the baselevels are of age more recent than the 

 Zapata epoch, but there is room for possible doubt in the case of the 

 highest terraces. 



When rifts such as those described have been seen in northern regions 

 some theorists have considered them evidences of glacial dams, but the 

 Cuban rifts are simply stream-made ravines deepened and widened by 

 sea currents breaking through the depressions during oscillation of the 

 land. 



SOUTH COAST OF THE ISLAND. 



The baselevel valleys, from 800 feet upward, in the Trinidad mountains, 

 record an elevation as plainly as the other terraces. They have been 

 uplifted so recently that they are not yet penetrated by the growth of 

 the youthful canj^ons (see figure 2, page 69). The recent terraces have 

 been confused with the frontal plains, such as those at Trinidad and 

 Santiago, which seem to be the product of wave action, modified when 

 at baselevels of erosion. This most important plain has an elevation of 

 about 100 feet at Cienfuegos, 200 to 240 feet at Trinidad and al)out 350 

 feet at Santiago (Kimball). This feature antedates the Zapata epoch, as 

 that formation overlaps the plains. However, there are lower terraces. 

 At Trinidad there is a sand terrace at 175 feet and anotlier at 50 to 60 

 feet, in whicli there is much gravel, and both of these shorelines are in- 

 scribed upon the Zapata series. A lower limestone terrace occurs at an 

 elevation of less than 10 feet in this part of Cuba. Two lower terraces 

 also occur at 175 and 14 feet in the vicinity of Santiago (Kim))all). In 

 the region of Baracoa these prominent terraces occur at about 500, 200 to 

 250 and 30 feet (Crosby). Professor W. 0. Crosby also describes baselevel 

 plains at 800 feet, and on II Yuinqui another at 1,800 feet. The base- 

 level valleys of the Trinidad mountains, at altitudes from 800 to 1,500 

 feet, as yet incised to only a moderate distance by canyons, indicate the 

 recent elevation of the mountains. 



From these data there appears to liave been considerable oscillation 

 during recent geological epochs, with a gentle deformation, raising the 

 •southeastern portion of Cuba higher than in the central, but sufficient 

 study of the terraces has not been made for working out their accurate 

 history, such as whether they belong to one or two epochs. That their 

 elevation is recent is shown by the small streams having lately cut can- 

 yons everywhere along the coast, too lately to have been transfornied into 

 V-shaped valleys. 



