128 REVIEWS 



tiago de Cuba: orthofelsite porphyry (rhyolites) like those erroneously 

 referred to by the late Professor H. D. Rogers as "jasper," and later 

 recognized by the late Dr. T. Sterry Hunt as a mixture to which he 

 gave the general name " orthophyre," also like the Arvonian tuffs of 

 Hicks near St. David's Head, Pembrokeshire, Wales. 



D. The specimens from the region of the La Plata mines were 

 quartzites containing hornblende, iron ores, and among the incidental 

 minerals a claret-red garnet. 



In the area described were found upon or associated with the erup- 

 tives sandstones, conglomerates and crystalline limestones, laminated 

 iron ores with masses of pyrite not yet converted into the latter. The 

 alteration of the areas of contact in these rocks by the more recent 

 diorite dykes which cut them was evident. 



From the zoological and geological researches of Alexander Agassiz 

 in Caribbean and Mexican waters, and the careful studies by Gabb, 

 Crosby, Spencer, and Hill, the probability of very great changes of 

 level in the Antilles since the close of the Cretaceous period is forti- 

 fied by several different lines of proof, /. e., the ledges and shelves of 

 the island borders, the wide distribution of the white radiolarian 

 limestones, etc. Professor Crosby pointed out orographic reasons for 

 assuming a former " bridge " (/. e., causeway) between the greater and 

 lesser Antilles. As he says, the mountains of "the northern arm of 

 the island of San Domingo pointing toward Cape Maysi on Cuba," 

 and the northern range in Cuba "regains the western trend and 

 points directly toward Yucatan." He also alludes in his paper of 

 December 13, 1882, to the "axis of old eruptive rocks," of which, so 

 far as he has been able to learn, "each member of the group consists." 

 He does not give his authority for the fact, nor say to what age he 

 ascribes these eruptives ; but if he contem.plated the possibility of this 

 age being pre-Cambrian, he anticipated by six years two of the 

 strongest reasons I adduced for belief in the physical continuity of the 

 great and little Antilles, and the present exposure of parts of the 

 nucleus which are of great age and possibly have never been very 

 deeply covered by sedimentary rocks. 



His observation that this nucleus is flanked on either side by schists 

 and slates I have confirmed, and I have been tempted to class these 

 with the damourites of the Appalachians, and the feldspar porphyry 

 (rhyolites), with the Arvonian tuffs of South Wales. 



'^ Zar Geologie von San Domingo. Abh. der natiirw. Gesel. "Isis" in Dresden, 

 1897, Heft ir, p. 64). 



