watxott.J SUMMARY NORTHERN APPALACHIAN. 275 



NORTHERN APPALACHIAN DISTRICT. 



The Northern Appalachian District includes the Hudson River and 

 Lake Cham plain area, east of the river and lake, and an extension 

 northeastward into Canada as far as the vicinity of Cape Rosier on the 

 Gulf of St. Lawrence. 



The geographic distribution of the Cambrian strata of the Northern 

 Appalachian District, south of the Canadian extension, is deline- 

 ated on a geologic map of eastern New York and western Vermont 

 published in 1888 by Mr. C. D. Walcott. 1 On this map the " Gran- 

 ular Quartz," "Red sandrock," "Georgia slate," and Potsdam sand- 

 stone are differentiated as far as the known data would permit. 

 The stratigraphic relations of the various divisions in Vermont are 

 shown in a series of sections by Prof. C. H. Hitchcock, 2 and for New 

 York by a section on the above-mentioned map. 



The "Granular Quartz" is found on the western side of the Archean 

 rocks, from southeastern New York and western Connecticut northward 

 to Massachusetts, and into Vermont nearly to the Canadian border. The 

 exposed outcrop is more or less interrupted because of the removal of 

 the rock by erosion or its concealment by superjacent deposits. 



Jn Vermont the " Granular Quartz" is a very compact, hard rock that 

 passes into a number of varieties. It is described in the Geology of 

 Vermout 3 as granular, gray, or reddish quartz rock; fine granular or 

 arenaceous quartz rock : granular porous quartz, or pseudo-buhrstone ; 

 quartzose aggregate ; quartzose breccia ; quartzose and micaceous con- 

 glomerate. There are also associated with it talcose and mica schists 

 and limestone. The quartzite is remarkably compact and enduring, 

 and it occurs in bowlders all over the southern part of Vermont, in 

 Massachusetts, New York, and Connecticut, many miles from the parent 

 ledges. Along the range of the rocks the bowlders cover the surface, 

 and in some instances this is the ouly way jn which the line of outcrop 

 of the formation is indicated. Details of the geographic distribution 

 in Vermont are given in volume 1 of the Geological Survey. A sec- 

 tion of 973 feet was measured in East Dorset by Prof. C. H. Hitchcock, 

 and the thickness of the formation in Vermont is estimated at 1,000 

 feet. It retains its essential characters in passing southward into 

 Massachusetts, New York, and Connecticut. 



On the western summit of Clarksburg Mountain, northeast of Wil- 

 liamstown, the basal bed of the quartz series is a conglomerate, resting 

 uuconformably upon pre-Cambrian gneiss. The conglomerate is suc- 

 ceeded by beds of quartzite, usually compact, hard, fine grained, and 



1 The Taconic system of Emmons and the use of the name Taoonic in geologic nomenclature. Am. 

 Jour. Sci., 3d ser., vol. 35, 1888, pp. 229-242, 307-327, 394-401. 



'Geological sections across Vermont and New Hampshire, Am. Mus. Nat. Hist. Bull., vol. 1, 1884, pp. 

 155-179, pL xvi. xvii. 



3 Hitchcock, C. H. Hypozoic and Paleozoic rocks. Report on the geology of Vermont, voL 1, 1861, 

 p. 342. 



