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



events following the Matanzas epoch seems- to justify the classification, 

 and, further, it is in accord with that which places the Lafayette of the 

 continent at the close of the Pliocene, for the loams of the southern 

 states and the limestones of Cuha occupy the same geomorphic position. 

 On the continent the loams were derived from the enormous supply of 

 the residual soils, but in Cuha there were few islets left above the sea to 

 supply mechanical material to the Matanzas formation. 



GEOGRAPHIC FEATURES OF THE PLIOCENE PERIOD. 



Already references have been made to the enormous erosion preceding 

 the deposition of the Matanzas limestones, producing a degradation far 

 greater than any since the pre-Cretaceous times. The pre-Matanzas de- 

 nudation in Cuba is in keeping with that of the pre-Lafayette epoch of 

 the continent, where during the epoch of the great erosion, valleys several 

 miles in width and hundreds of feet in depth were excavated out of the 

 often incoherent formations, ranging from the lower Cretaceous to the 

 U2:)per Miocene strata. In short, the Pliocene period was one of general 

 elevation of the land. This is shown in the Havana valley, where the 

 Tertiary limestones were in many places completely removed before tlie 

 Matanzas subsidence. The Yumuri valle}" at Matanzas city illustrates 

 the Pliocene erosion. It was excavated out of Eocene and Miocene lime- 

 stones to a depth of about 400 feet and a width of three miles, and was 

 afterward partly filled with the Matanzas formation, of which fragments 

 only now remain in the valley (see figure 12, page 92). The work of 

 denudation was not that of a large river, but of the warm troi)ical rains 

 and rills whose efficiency upon the porous calcareous rocks and sands 

 far exceeds that suspected b\^ one who has not visited the tropics. The 

 amount of denudation is seen in all the large valleys and over the plains 

 of central Cuba, where the Matanzas formation occui)ies the hollows i)ro- 

 duced by the earlier Pliocene erosion. From the extent of erosion, evi- 

 dently removing great ridges, and the structure of the valleys, the con- 

 clusion is formed that the duration of high elevation lasted for a long 

 time, and that the altitude was great, probably sufficient to excavate 

 great valleys, but their great depth now submerged was only completed 

 during the next period of erosion. With the following subsidence to 400 

 feet, more or less, only a few small islands remained. Indeed, from the 

 study of the geomorphy it would appear that the mountains then rose 

 to much more moderate elevations above the sea than at the present time. 



Pleistoct:ne History. 

 zapata formation. 



To the series of red loams and water-worn gravels which succeed the 

 Matanzas the writer has applied the name Zapata formation. The name 



