398 PROCEEDINGS OF THE ACADEMY OF [MaV, 



He also alludes in Ms paper of December 13, 1882, to the "axis of old 

 eruptive rocks" of which, so far as he has been able to learn, " each mem- 

 ber of the group consists." He does not give his authority for this 

 statement nor say to what age he ascribes these eruptives; but if he 

 contemplated the possibihty of its being pre-Cambrian he anticipated 

 by six years two of the strongest grounds for my 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 covered by sedimentary rocks. 



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

 and slates has been fully confirmed, and I have been tempted to class 

 these with the mica schists of the Appalachians, and the feldspar por- 

 phyry (rhyohtes) with the Arvonian tuffs of south Wales. 



Dr. W. Bergt strongly supports the Archean age of the nucleal 

 axis of San Domingo if not of all the Caribbean Islands in the follow- 

 ing words ■? 



"Das archaische Alter welches P. Frazer fiir die Centralketten des 

 siidostlichen Cuba feststellen konnte, und das er fiir ganz Jamaika, 

 fiir San Domingo, Puerto Rico, und die Windwardinseln vermuthete, 

 kann nunmehr bestimmter fiir San Domingo angenommen werden." 



It may be, as Mr. Hill suggests, that no "Paleozoic nucleal rocks" 

 have been established with certainty in "Cuba and Santo Domingo" 

 or any other of the border lands of the "American ^Mediterranean,"^ 

 although de Castro imagined he had discovered such near Cienfuegos, 

 yet this fact would not preclude the possibility that part of these 

 nucleal rocks are pre-Cambrian. 



To summarize the observations: 



(1) There is a complex of diorite, felsite and rhyolite forming the 

 axes of the mountain ranges of eastern Cuba. 



(2) With these are associated schists which in places assume a 

 gneissoid character. 



(3) The diorite and the clastic rocks resting on it are traversed by 

 numerous veins of later eruptives, on the contact planes of which latter 

 many phenomena of alteration may be observed. 



(4) No such indications of alteration are apparent at the contacts 

 with the older diorite mass, but, on the contrary, the sedimentary rocks 

 seem to have been deposited upon it without disturbance. 



^ "Zur Geologic von San Domingo." Abh. der naturw. Gesel. "Isis" in Dresden, 

 1897, Heft II, p. 64. 

 ^ Cuba and Porto Rico, p. 384. 



