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



of the Zapata series. Indeed, some of the low and poor country between 

 Colon and Santo Domingo apparently belongs to this formation. 



The resemblance of the gravels to the similar formations in the south- 

 ern states was noted b};^ Mr Mathew, who saw the likeness to Hilgard's 

 orange sand long before it was differentiated into the several members 

 now known. 



Along the Sagua le Grande river, near the city of the same name, rest- 

 ing upon the eroded surfaces of the Matanzas and other Tertiary lime- 

 stones, there are about 20 feet of impure sand and fine gravel and some 

 layers of pebbles, the whole forming the floor of an extensive plain. In 

 places the layers are horizontal, but in others the beds dip at low angles 

 toward the northeast. These ])eds appear to be equivalent to those at 

 Cienfuegos. 



In the Yumuri valle}^ west of Matanzas, beds of the gravel were seen 

 at several places, but not at any altitude above 100 feet. These surface 

 deposits also occur at Havana. 



GEOGRAPHIC FEATURES OF THE PLEISTOCENE PERIOD. 



The old-fashioned method of reading the history of the eartli by the 

 succession of the coats of the geologic onion has been followed, but the 

 more important history is that recorded in the breaks and unconformities. 

 When these are studied over large areas we find very broad valleys which 

 have since been filled by the later deposits. In the Havana valley, in 

 the Yumuri valley, and over tlie plains of central Cuba there is abundant 

 evidence of the enormous degradation to which the island has been sub- 

 jected, for valleys several miles in width have been excavated since the 

 Matanzas epoch, even to depths of hundreds of feet. Thus the Yumuri 

 valley was reexcavated during the early Pleistocene elevation to its origi- 

 nal or greater size. These valleys continue into the fiords, such as that 

 of Matanzas bay, which have been excavated or reopened since the 

 Matanzas epoch. Other examples of the post-Matanzas erosion are seen 

 in the formation of the bays of Cienfuegos (see figure 10, page 91) and 

 Santiago (see figure 9, page 90). The Cienfuegos harbor was formed be- 

 tween the close of the Matanzas epoch and that of the deposition of the 

 Zapata loams. All of these valle3's show the great elevation when the 

 fiords were reoi)ened upon the removal of the Matanzas beds which partly 

 filled them. This elevaton, as shown by the Cuban fiords, alone suggests 

 a late altitude of more than 7,500 feet, as seen in the gulf of Cazones. 



In the subsidence from the liigh altitude there was rest long enough to 

 form the baselevel terraces underlying the Zapata formation at Trinidad, 

 at Matanzas and the plains of the central part of the island. The Zapata 

 subsidence is not known to have exceeded 240 feet below the present level, 



