GENERAL STRUCTURE AND CORRELATION. 29 



tween the Archean (Laurentian) and Cambrian. Thus for only some ob- 

 servations that will serve as clews have been made in this direction. 1 One 

 apparently negative piece of evidence may be seen at the place where the 

 Archean rocks of the New York highlands suddenly end near Poughquag, 

 Dutchess county, New York. Here the highlands end in a promontory 

 of nearly vertical beds of old gneisses, against which the Cambrian quartz- 

 ite lies with a very flat dip. 



Toward the correlation of the Green mountain rocks with the fossilif- 

 erous strata of New York, the paleontologists have given us s:nne facts. 

 Mr Walcott's discovery of < )lenellus casts in the quartzite of Clarksburg 

 mountain, about 100 feet above its base, caused him to assign that rock to 

 the Lower Cambrian. The many findings of Lower Silurian fossils in the 

 limestone of Vermont have shown that limestone to include Calciferous, 

 Chazy, and Trenton horizons, and it is inferred that, since the limestone is 

 Trenton and is capped by schists, the latter are of the age of the Utica and 

 Hudson River slates. 



I have shown above that the white gneisses and conglomerates of 

 Hoosac mountain are the equivalents of the Cambrian quartzite and that 

 the albitic schists of Hoosac mountain represent in time both the limestone 

 and schists of the valley, and therefore range from the Cambrian into or 

 through the Hudson River. 



It seems probable that the limestone must reach down well into the 

 Cambrian and that all of the Cambrian that is not represented by the 

 quartzite must, in the valley, be included in the lower part of the limestone 

 and its downward transition beds; 2 while on the mountain it must be in- 

 cluded in the lower beds of the albite schists. 



We have vet to discover whether the nonfeldspathic schist of the 

 eastern portal of the tunnel (Rowe schist) represents Hudson River, or, 

 perhaps, .Medina time. Geologically above the nonfeldspathic schists of 

 the eastern portal, and coming in successively to the east to build up the 

 old plateau region that forms properly the eastern belt of the Green moun- 



1 Since this w as « ritten » e have found Algoukinn schists at several points along the Green moun- 

 tains. 



• Tins luis been confirmed by recent discoveries of Cambrian fossils in the lower jiart of the lime- 

 stone near Rutland and Clarendon, Vermont, bj Messrs. Foerste, Wolff, and Dale. 



