hill: geology of Jamaica. 191 



them in the form of so called dynamometamorphic phenomena; "ac- 

 cordingly they have to be regarded as * older ' until their younger age 

 has been unassailably demonstrated, which is hardly to be expected. 

 The crystalline schists, the last of which might be given considerably 

 greater fulness by collections and observations not merely occasionally, 

 but systematically, bear in no wise the character of contact metamor- 

 phism ; they have to be regarded as normal Archaean rocks, though, like 

 the older massive rocks, they are in part altered by mountain pressure 

 and folded on a small scale." 



Thus, according to Bergt, in San Domingo, besides the younger strata 

 of the Cretaceous and the Tertiary, as the bed rock, there is possibly 

 Archaean plexus. 



Bergt and Frazer's conclusions, as far as they apply to Santo Domingo 

 and Cuba, may be correct, for there are other reasons for believing that 

 here and there in the main Antillean chain there are evidences of a 

 Pre-Cretaceous buttress, but there is absolutely no stratigraphic evi- 

 dence as yet unearthed to warrant the assertions that similar rocks 

 occur in Jamaica, Porto Eico, or the Windward Islands, where as yet 

 no such rocks have been found, although, except in the last named, the 

 clastic and terrigenous nature of the basement exposures certainly indi- 

 cate the pre-existence of rock masses of older age than those now known 

 in situ. The younger eruptive rocks of San Domingo enumerated by 

 Bergt are most probably of Cretaceous and Tertiary age. 



Omitting from further consideration the Pre-Cretaceous crystallines, 

 the interpretable volcanic phenomena of the AVest Indian Islands and 

 the bordering continental lands may be classified for historical purposes 

 into the following time categories : — 



1. Regions where there are no visible signs of vulcanism : Eastern 

 Coastal Plain of the United States, Bahamas, Barbados. 



2. Regions where vulcanism existed prior to the beginnings of the 

 later Mesozoic : The Cordilleras of North America, Guatemala, Oaxaca, 

 and Andes, and possibly Cuba and Haiti. 



3. Regions in which vulcanism was greatest in late Cretaceous and 

 early Tertiary time : Mexican Plateau, Western Coastal Plain, Panama, 

 north coast of South America, Great Antilles. 



4. Regions where vulcanism was active in middle Tertiary time, since 

 which it has been quiescent : Panama, north coast of South America, 

 and Antilles. 



5. Regions of recent volcanic activity : Southern Mexico, Central 

 America, Northern Andes, and Caribbee Islands in part. 



