hill: geology of JAMAICA. 19 



o 



Some time during the middle of the Tertiary time — probably betweeu 

 the Vicksburg and Bowden epochs, as we have elsewhere shown — the 

 great intrusion of granitoid and dioritic porphyritic rocks occurred in 

 Jamaica. The dioritic dikes were probably slightly subsequent to the 

 granitoids in sequence, but they are both so intimately associated as to 

 be practically inseparable, and hence may for discussion be considered as 

 a unit. There is little evidence, excepting in the case of the Low Lay ton 

 basalt, that the igneous rocks of this epoch ever protruded to tlie sur- 

 face in Jamaica although they may have done so elsewhere. In Cuba 

 there is evidence presented by Kimball ^ that eruptive diorites overflowed 

 the aid Eocene limestones (called corallines by him) of the Sierra Maestra. 

 In the vicinity of Havana the Vicksburg limestones are also cut by 

 Tertiary intrusives. 



There is abundant evidence that the Mid-Tertiary vulcanism was far 

 reaching in extent and affected all the Great Antilles, Virgin Islands, 

 Yucatan, Costa Rica, and the Panamic, Colombian, and Venezuelan coasts 

 of the Caribbean. A brief outline of the distribution of these phe- 

 nomena on the mainland has already been presented in my Panama 

 report.'^ Kimball ^ has described with considerable detail their occurrence 

 on the Santiago coast of Cuba. Descriptions of San Domingo by Gabb,* 

 and of Porto Rico, the Virgin Islands, and St. Bartholomew by Cleve,^ 

 also confirm this opinion. Rocks of this general age also occur in St. 

 Martin, Burks,* Coopers, Georges, Round Rock, St. Croix, St. Thomas, 

 Tortolu, and Salt Islands. Cleve doubtfully refers them to the Creta- 

 ceous or Eocene ; but after reading his observations in the light of our 

 own researches, there can hardly be the least doubt that they are of the 

 same age as the similar phenomena of the Antilles. 



With the possible exception of the Low Layton stock of Jamaica, 

 which may or may not have been an accompanying event, these rocks 

 represent the last indications of vulcanism in the Great Antilles and 

 Virgins — where there is no evidence of igneous activity — in the subse- 

 quent epochs of late Miocene, Pliocene, Pleistocene, or recent time. 



The Caribbee Islands constitute a unique and peculiar volcanic 

 province, the discussion of which, with their general phenomena, can 

 now be briefly considered. To those who first look at the map and have 

 not considered their minute geology, the Lesser Antilles, extending 

 across the east end of the Caribbean from Porto Rico to South America 



J Amer. Jour. Sci., Vol. XXVIII. pp. 419, December, 1884. 

 2 Loc. cit., p. 251. 8 Loc. ciL, pp. 416, 417. 



* Geology of San Domingo, p. 83. ^ £qc. cit., p. 47. 



VOL. xxxiv. 1.3 



