652 



BROVVX AND O COXXELL THE JURASSIC OF CUBA 



even older, beds come in, while each formation thickens westward. The 

 stratigraphic relation is clearly that of a marine transgressive overlap 

 toward the east, the late Middle Jurassic sea having encroached upon 

 the western end of the Cuban landmass, which continued to sink through 

 late Jurassic time. The individual divisions of the rock series are thick- 

 est in the Vihales region, and thin out eastward, while the basal con- 

 glomerate occupies a diagonal position and becomes progressively younger 

 toward the east, as indicated in the restored cross-section (figure 13). 

 Above the Jurassic rocks are about 1,000 feet of irregular, discontinuous 

 limestones with thick beds of dark-colored shale in the upper measures 



Figure 12. — Folded Schists North of the Limestone Mountains on the Road to Esperanza 



and lighter-colored marly shales with sandstone strata near the base. 

 Numerous Rudistes attest the Cretaceous age of these beds, which also 

 contain gastropods, Ostrea and other pelecypods. Submergence must, 

 therefore, have continued through Cretaceous time, although there may 

 have been a retreat of the sea at the end of Jurassic or in Eo-Cretaceous 

 time. 



At the end of Cretaceous time folding and tilting took place, the verti- 

 cal uplift being greater in the western part of the Province of Pinar 

 del Bio than in the eastern. These diastrophic changes probably con- 

 tinued throughout the Paleocene and were synchronous with similar 

 movements in many other parts of the world at that time. During that 



