78 J. W. SPEXCER — GEOGRAPHICAL EVOLUTION OF CUBA. 



It should be noted that the shells are only preserved in the form of 

 casts, and this condition renders their specific determination difficult, but 

 Doctor Dall says he has no doubt of the age of the assemblage of fossils. 



There is a strong lithologic difference in the characters of the strata 

 above and below the line where the division between the Miocene and the 

 Eocene is placed. The Eocene beds bear a close resemblance to the fossil- 

 iferous strata near Havana, and, indeed, to the Vicksburg beds of the 

 southern states. If the lithologic separation of the two divisions of the 

 Tertiary strata be not wholly supported by the paleontologic, yet it has 

 no bearing on the sequence of physical events presented in this study. 



At several points along the Union railway between Matanzas and Ha- 

 vana good sections of the Tertiary formations are exposed in the sides of 

 the valle3"S. The strata dip at only moderate angles, but several anti- 

 clines and synclines were observed, such as those seen near San Miguel. 



Havana region. — Salterain has treated the Tertiary rocks at consider- 

 able length in his studies about Havana. Like the rocks at Matanzas, 

 the Eocene limestones are harder and more siliceous than the Miocene 

 deposits. The strata form ridges along the coast and appear conformable. 

 The lower beds unconformably succeed the Cretaceous strata already 

 described. The beds dip at from 12° to 15° northwestward. The Miocene 

 beds are earthy, as at JNIatanzas, and in part porous with the fossils in 

 the form of casts or moulds. From five quarries Salterain collected forty 

 species of Miocene fossils, and from seven other localities he obtained 

 forty-four species of Eocene forms. The lists of these fossils appear in his 

 paper, and Doctor Dall considers that the respective formations were 

 correctly defined. 



Owing to the proximity of the Tertiary formations to the sea, the 

 streams have excavated a l)road amphitheater out of the elevated plateau 

 so that in the erosion of the Havana basin the Tertiary formations have 

 been largely removed , witli the consequent exposure of the Lower Creta- 

 ceous and other beds. According to Salterain's estimate, the Eocene beds 

 aggregate 200 feet and the Miocene 160 feet. These estimates exclude all 

 of the limestones which were involved in the post-Cretaceous disturb- 

 ances. Near a quarry southwest of Havana there is an isolated mass of 

 conglomeratic limestone dipping 30° southwest, or at a greater angle and 

 in another direction than that 2)revailing in the Tertiary limestones. 

 The Tertiary limestones give rise to a residual soil like red loams. 



Sagua le Grande region. — This is a leap of 150 miles to the east of Ha- 

 vana to a locality situated on the northern side of the island. In this 

 part of the island the country is a low- plain of great extent, out of which, 

 southwestward of the city, low ridges rise. These ridges are composed of 

 Tertiary limestones with their surface greatly eroded, and often levelled 



