
68 The American Naturalist. [January, 
. If this mass had resulted from volcanic outflow there must have 
been contact phenomena, and changes induced on the surfaces of the 
rocks with which it was brought in contact. No such contact alter- 
ation has been observed between these rocks and those of either the 
Paleozoic, Mesozoic, or Czenozoic groups which in different localities 
meet them. 
8. The direction of the range, considered as a whole, lends support 
to the hypothesis that it is a fork of the Andes which, diverging from 
the main axis in Guatemala, traverses the peninsula of Yucatan, and A 
in a symmetrical curve sweeps through the highlands of Cuba and 
Jamaica, Hayti, Puerto Rico, the Windward Islands and the northeast 
coast of Venezuela. This rim of high land once enclosed the Carib- 
bean as another Mediterranean Sea, 
g. The shapes of the hills of this range, produced by weathering, 
are not those usually visible in regions of volcanic, but rather of meta- 
morphic rocks. 
The rocks which furnished the basis for the above conclusions are 
all, or nearly all, alteration products. In some cases they appeared 
to be the results of a series of metamorphoses, some of their constit- 
uents seeming to pass through cycles of change, ending in the : 
mineral with which the alteration began after a number of intermediate 
stages. The rocks are diabases or diorites, with epidote, porphy- 
ritic dolerites, which resemble and have been taken for syenites; 
garnet rock; actinolite ; felsite and orthofelsite porphyry, like that 4 
of the South Mountain of southeastern Pennsylvania, of St. Davids | 
Head in Wales, and elsewhere. To these are added pyrite, and iron — x 
ores and crystalline limestone. Copper and manganese ores are not 
rare, but their relations to the rocks under consideration have not been 
made out. 
Note.—A number of the first petrologists of Europe who have ex- 
amined the slides are disposed to consider the specimens of not — 
later than Paleozoic age, while none are willing to deny that they 
may be earlier. 


