1886.] NEW TOEK ACADEMY OF SCIENCES. 13 



George. The rock is very similar to that from the bottom of the 

 deep well at Bischoff^s Brewery. 



The serpentine and talcose rocks which form the ridge through 

 the central part of the island have been re-examined with c n 

 sideiable care. It will be remembered that in my first com— 

 miinieution I regarded these as metamorphosed magnesian 

 limestones. In the course of the discussion which followed my 

 second paper, Dr. Julien expressed his opinion, based on micro- 

 sco|)ical studies of the rock, which revealed the presence of 

 much partially altered amphibole, that they are derived from 

 hornblende schist, and the specimens from the deep well-boring 

 above alluded to, being certainly partially hydrated and other- 

 wise altered, gave support to his hypothesis. It now seems to 

 me probable that both of these suppositions are in a measure 

 correct: that the serpentines and associated rocks have been 

 produced by the extensive alteration of both limestones and 

 hoi-nblendic, or rather tremolitic, strata, and that schists as well 

 have furnished some of the material for their construction. 

 Tliis conclusion is now reached from the following considera- 

 tions: 



1. There is no proof whatever that these serpentines are 

 metamorphosed igneous rocks. We have failed to detect any 

 olivine-like minerals in them; and in this respect they appear to 

 differ from the area near Baltimore recently described by Prof. 

 "Williams in Bulletin No. 28 of the United States Geological 

 Survey. Messrs. Whitney and Wadsworth, in their discussion 

 of azoic rocks in the Bulletin of the Museum of Comparative 

 Zoohtgy, Vol. VII., pp. 464-465, state that it seems more 

 reasonable to them to ascribe an igneous origin to the rock in 

 the region under consideration, because a large part of the 

 thoroughly studied serpentines of the world have been proved 

 to be tlie result of the metamorphism of igneous masses. It 

 does not appear that these writers have ever visited the area, 

 nor, indeed, that they have examined any of the I'ock. As it 

 has been stated on good authority that the concluding portions 

 of Messrs. Whitney and Wadsworth's paper, dealing with a 

 proposed classification of pre-Silurian rocks, were not meant to 

 be taken as their actual ideas on the subject, but intended as a 

 joke (though if this be so, it would have saved much unneces- 

 sary thought and trouble had they designated it thus), and as 

 the general tendency of their paper appears to be to criticise 

 every investigator's work without furnishing any more valuable 

 suggestions than have been advanced, we must confess to some 

 doubt as to Messrs. Whitney and Wadsworth's actual position. 



2. There is abundant evidence that these rocks are stratified, 

 though this feature cannot be made out in every outcrop. The 



