1886.] NEW TOKK ACADEMY OF SCIENCES. 15 



similar to ''mountain leather" on Staten Island. The cleavage 

 of the serpentine is much like that of the limestones, and on the 

 -cleavage faces of the latter there is often seen a development of 

 tremolite, while on the serpentine faces there is considerable 

 amianthus. 



The parallel metamorphisni of schists in the production of 

 these serpentines is indicated in the occurrence on Todt Hill, 

 Staten Island, of a very soft, schistose rock, apparently now 

 chloritic, containing altered crystals of tourmaline, a mineral 

 quite abundant in the schists of New York Island. 



As regards the relative position of the serpentine to the gran- 

 itic rocks on Staten Island, I have no new observations to record 

 and do not think that the exposures admit of more plausible 

 explanation than the hypothesis advanced by me in my original 

 communication, where the serpentine was regarded as overlying 

 the other rock, and is so represented in my diagrammatic sec- 

 tions. There is certainly no other rock exposed within the ser- 

 pentine area laid down on my map. Of course, this considera- 

 tion applies to the Staten Island outcrops alone ; elsewhere they 

 are inclosed by the gneisses, etc., and this superposition does not 

 occur. Doubtless the Staten Island rocks were originally depos- 

 ited in a conformable sequence, but the serpentines were left on 

 top in the folding of the strata. The idea advanced by me that 

 the serpentine ridge is an anticlinal fold must be abandoned in 

 the light of more recent investigations; it is quite evidently 

 made up of a series of smaller folds which, collectively, are more 

 probably of synclinal structure, though the exposures are not 

 sufficient to satisfactorily settle this question. 



In my original paper, I stated that these crystalline rocks of 

 Staten Island probably extend southwestwardly across New Jer- 

 sey to Trenton, forming an axis which marks approximately the 

 junction of the Triassic and Cretaceous formations. This imag- 

 inary axis was indicated on the accompanying maps and sections. 

 Proof of the general truth of this hypothesis is now furnished 

 from a well recently bored near Perth Amboy, which reached 

 gneiss at a depth of seventy feet. This was immediately over- 

 laid by Triassic red shale, about twenty feet in thickness, the 

 latter covered by Cretaceous clay and sand, pre-glacial drift 

 and morainal deposits. A note on this well may be found in the 

 annual report of the State Geologist of New Jersey for 1885. It 

 will be noticed that here the Triassic strata are comparatively 

 thin, and this point is doubtless very near its southeastern 

 margin. 



I have regarded these metamorphic rocks as Archaean, and 

 have thus alluded to them. I am well aware that they are by 

 others considered to be of Lower Silurian age, and that this the- 



