1% 



119 



Trans. M Y. Ac. Sen 



Soluble in Hydrochloric Acid. 



SiOj. 

 AI0O3 

 FeaOg 

 MgO. 

 CaO . 



SOa.etc. 



Soluble 



Insoluble 9 



Water and COo 



Totals. 



The analyses show a nearly uniform composition for the entire thick- 

 ness, and the only marked difference from the unaltered sandstone is in 

 the soda. Whether this is the remains of a triclinic feldspar or not, I 

 do not feel confident to claim, as the granytic areas, forming the basin 

 in which the Triassic beds of the Eastern States lie, and from which we 

 have supposed them to be derived, are not albitic in character, except 

 in some very local instances. However, in a formation of this character, 

 the content of soda is generally attributed to albite, of which, from the 

 analysis, it would seem that there is from fifteen to twenty per cent, 

 present in the disintegrated sandstone, and about fifty per cent, in the 

 unaltered. These are very appreciable proportions and quite constant 

 throughout the Triassic stratum. By our latest calculations the thickness 

 of this seems to reach at least twenty-five thousand feet, on the western 

 side of the uplifted granytic area, which separates the Triassic deposits 

 represented in New England and in the South Central States. 



DISCUSSION. 



The President stated that the rock in question was called arkose, 

 but often so rich in feldspar as to be a true feldspathic sandstone. 



A MEMBER remarked that an outcrop of the same rock, in en- 

 tirely unaltered condition, occurred all along the eastern foot of the 

 Palisade range, from Jersey City to Weehawken. The absence of 

 albite might possibly have been derived from the degradation of some 

 albitic granyte on the shore of the Triassic sea, though he was not 

 aware of the occurrence of such a rock in the Laurentian of 

 Northern New Jersey ; more probably it had been caused by the 

 entire decomposition of the ferruginous orthoclase in the granyte 

 derived from that region, with the corresponding concentration of 

 the associated soda-feldspars. 



Mr. Darton referred to the existence of albitic granytes near 

 the borders of the Triassic basin in Virginia, etc. 



