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



same time the erosion has developed bold reliefs, so that the serratures 

 of the surface are dependent upon the durable remnants of the upturned 

 strata. No conglomerates were observed in the exposures visited. 



Whatever their age, the Trinidad mountains constitute the oldest rocks 

 of central Cuba, but the formations were generally removed b}^ denuda- 

 tion before the later accumulations, which are nowhere else penetrated by 

 similar rocks. Where the mechanical materials of the Trinidad moun- 

 tains came from, whether from strata since buried beneath newer deposits 

 or from the continental extensions, cannot now be determined. 



IGNEOUS FORMATIONS. 



Forming some of the ridges and also the rugged valleys there are dio- 

 rites and disturbed strata of serpentine, all of which are greatly decayed 

 where the natural surfaces are exposed. There are also a few granitic 

 rocks. These formations are included within the area of Cretaceous 

 distribution and have been exposed in narrow belts in many portions of 

 the island, and farther east in broader zones, on account of the removal 

 b}^ denudation of the overlying Cretaceous and Tertiar}- formations. The 

 characters of the rocks appear constant, so that their history in one part 

 of Cuba may probably be applied to the whole island, 'i'he ui)turned 

 beds of serpentine have been extensively quarried at Havana, and the 

 formation can be seen in the Yumuri valley near IMatanzas, near Xagua 

 bay, about Santa Clara, etcetera. The igneous rocks underlie Cretaceous 

 dei)osits, but nothing is definitely known of their age, so that they may 

 belong to the early Cretaceous or to older formations. 



Cretaceous History. 

 local geologic characteristics. 



In general. — At the connnencement of this period, so far as the records 

 have shown, there were onl v a few insular masses of limestones and me- 

 chanical deposits in central or, indeed, most of Cuba. There were prob- 

 ably some islands of igneous rocks, but generall}^ these are only exposed 

 by subsequent denudation. 



Trinidad region. — I^^ying against the eastern Hanks of Trinidad moun- 

 tains and constituting much of the floor of Trinidad valle}^, there are ex- 

 tensive accumulations referable to the Cretaceous S3^stem. The lower 

 members are calcareous, glauconitic and gray sand or friable sandstone, 

 composed of ])oth angular and water-worn grains of quartz. They are 

 frequently exposed at the base of the Tertiary limestone ridges which 

 separate the valley from the sea. At the railway bridge west of the city 

 of Trinidad the beds dip 30° south, 25° to 45° west. Owing to the varia- 



