HILL: GEOLOGY OF JAMAICA, 191 
them in the form of so called dynamometamorphie 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 Archeean 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 
Archean 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 Rico, 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 voleanie phenomena of the West Indian Islands and 
the bordering continental lands may be classified for historical purposes 
into the following time categories: — 
l. Regions where there are no visible signs of vulcanism: Eastern 
Coastal Plain of the United States, Bahamas, Barbados. 
2. Regions where vuleanism existed prior to the beginnings of the 
later Mesozoic: The Cordilleras of North America, Guatemala, Oaxaca, 
ànd Andes, and possibly Cuba and Haiti. 
3. Regions in which vuleanism 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 vuleanism 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. 
