TRANSACTIONS OF SECTION C. 655 



The considerations which support this view are — 



1. Microscopic analysis shows immense alteration to have taken place, and con- 

 sequently a very long period to have elapsed. 



2. The complexity of the congeries of rocks forbids the hypothesis of their 

 La\-ing been derived from one mass. Where this congeries, therefore, is uncon- 

 formably adjacent to the Tertiary, there can be do reasonable doubt that the crys- 

 talline rocks are the elder. This point of view was suggested bj^ Mr. Teall, who 

 would consider the argument valid also for the contact with the Cretaceous, and 

 perhaps older series. It is difficult to see why it should not hold equally good for 

 the contact between these crystalline and the Paleozoic rocks as made out by De 

 Castro near Cienfuegos, Sec. 



3. The characters of the several associated rocks are those which one finds 

 united in very many Archean regions throughout the world. 



4. The products of alteration of these rocks are similar to those which one finds 

 in the districts just alluded to. 



o. The chemical peculiarities of the iron ores found in contact with these rocks 

 are similar to those which one finds in the ores of the Archean regions, both in the 

 low percentage of phosphorus and in the pyrite and (more sparingly) chalco- 

 pyrite disseminated through the ore, and in other respects. 



6. If this nucleal mass had been forced up from the earth's interior in a state 

 of igneous fusion there would not be now (as there are) abundant traces of strati- 

 fication and structure, implying an original sedimentation. 



7. If this mass liad 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 alteration has been observed between 

 these rocks and those of either the Paleozoic, Mesozoic, or Cenozoic 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 in a symmetrical curve sweeps 

 through the highlands of Cuba and Jamaica, Hayti, Puerto Bico, the Windward 

 Islands, and the N.E. coast of V'enezuela. This rim of high land once enclosed 

 the Caribbean as another Mediterranean Sea. 



9. The shapes of the hills of this range, produced by weathering, are not those 

 usually visible in regions of volcanic, but rather of metamorphic 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 constituents 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 of the South Mountain 

 of South-eastern Pennsylvania, of St. David's Head in Wales, and elsewhere. To 

 these are added Pyrite, and iron ores and crystalline limestone. Copper and man- 

 ganese 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 examined their 

 slides are disposed to consider the specimens of not later than Paleozoic age, while 

 none are willing to deny that they tnai/ be earlier. 



8. On a Specimen of Quartz from Australia and TJiree Specimens of 

 Oligoclase from North Carolina exJiibiting curious Optical Properties. 

 By Dr. Persifor Frazer. 



Mr. George F. Kucz, Gemmist for Tiffany & Co., of New York city, and reporter 

 on the precious stones of the United States for the United States Geological 

 Survey, desires through me to call attention to these minerals, on the curious 

 optical properties of which a preliminary note appears in the ' American Jotimal 



