Merrill — Metamorphic Strata of S, /:. New York, 885 



The thickness of the basal member is at present indeter- 

 minate, as nothing has been found beneath it, and in the Hud- 

 : River Bection it is Been to descend belovc tide-level. The 



maximum thickness exposed is in Breakneck Mountain, of 

 which the summit is said to be 1787 feet above tide. What- 

 ever be the true height of the mountain, its central mass from 



tide-level to the summit consists of hornblende-gneiss, and 

 whether it be anticlinal or monoclina] in structure, an equiv- 

 alent thickness of this rock is exposed. 



The second member or [ro«- bearing Group, as Dr. Britton 

 lias stated, consists essentially of granulites, this name being 

 used by him and the present writer to describe Bubcrystalline, 

 well stratified metamorphic rocks composed principally of de- 

 trital quartz and feldspar. They are highly metamorphosed 

 arkoses, and differ essentially from the under-lying formation 

 in the absence of magnesia-iron silicates such as hornblende and 

 biotite. The comparative absence of silicate minerals contain- 

 ing irofl is indeed the conspicuous feature of this member taken 

 i whole. In some places, as at Garrisons, a pale yellowish 

 mica is present, giving the rock the semblance of a granite, 

 under which name it is quarried, and in close proximity to some 

 of the magnetite beds in New Jersey, biotite and hornblende 

 are quite abundant. This formation is at least 500 feet thick. 



The beds of magnetite appear to occur at various levels in 

 the second group and offer little evidence of their origin. If, 

 however, it were known that the rock which furnished the de- 

 tritus out of which these granulites were formed, contained 

 magnetite distributed through it in any appreciable quantity 

 there would be good reason for the conclusion that the magne- 

 tite beds of this horizon originated as beds of magnetic sand 

 concentrated by wave action. There is no indication that they 

 originated as bog ores. They are simply lenticular beds en- 

 closed by a stratified metamorphic rock formed of quartz and 

 feldspar sand and there is no adjoining rock of which the com- 

 poeition would >uggest that it is a metamorphosed soil. There 

 18, besides, no indication of a former land surface on which 

 these beds might have been formed. The only suggestion of 

 uric agency is in the apatite which occurs with the iron ores 



some of the mines and this, if it were organic, could have 

 been derived from marine organisms as well as from terres- 

 trial. It is not. however, by any means certain that this apatite 

 i- organic, since the mineral is a frequent accessory in various 

 eruptive rocks. 



The strata of Dr. Britton's schistose group and the lime- 

 >t<»n(.'> which, according to him, occur near the top of the 5< 

 olid member are found near the Hudson River, in Orange 



inty at Fort Montgomery, and in Putnam County between 



