wAL.ori.l SUMMARY NORTHERN APPALACHIAN. 277 



during early Cambrian times; the sediments vary from pare quartz 

 sand to mixtures of sand and argillaceous and calcareous mud. 



The "Red Sandrock" series is confined almost entirely to northern 

 Vermont, not appearing south of Addison County. In the northern 

 part of Addison County it comes into contact with and merges into the 

 "Granular Quartz" series. It has not been recognized in contact with 

 the Archean rocks of the Green Mountains. From this, and its having 

 less of the character of a shore deposit and from its occurring west of 

 the line of outcrop of the "Grauular Quartz," it is quite probable it is 

 a deeper water accumulation, though contemporaneous with the "Gran- 

 ular Quartz." The Georgia slates, in the town of Georgia and in north- 

 ern Vermont, are conformably superjacent to the " Red Sandrock." 

 -As the formation is traced to the south, the " Red Sandrock " series 

 disappears, and the Georgia slates and shales, with their interbedded 

 limestones and sandstones, represent the entire Cambrian section ; so 

 it is very probable that the Georgia series as found in southern Ver- 

 mont and eastern New York represents or is equivalent to the " Gran- 

 ular Quartz" and the "Red Sandrock." The " Granular Quartz " has 

 been described separately, but it is more convenient to unite the "Red 

 Sandrock" and the Georgia slates, because the sections usually show 

 the latter resting conformably upon the " Red Sandrock" series through- 

 out northern Vermont. The geographic distribution of the Canadian 

 extension of the "Red Sandrock" and the Georgia slates is shown ou 

 a map by Sir Wm. E. Logan, entitled "The distribution of the rocks 

 belonging to the Potsdam, Quebec, and Trenton groups of the east side 

 of Lake Champlain," accompanying an Atlas of maps and sections of 

 the Report of Progress of the Geological Survey of Canada for 18G3, 

 published in 18G5. The formations extend north of the boundary line 

 about 5 miles, where they appear to have been cut out by faults that 

 bring the superjacent formations into contact with them. 



The "Red Sandrock" series consists of white and red dolomites and 

 sandy layers. Some of the strata are mottled red aud white, and a few 

 are brick red or Indian red. Some beds contain a considerable amount 

 of siliceous sand, and all weather a yellowish or reddish brown. They 

 are also interbedded with gray argillaceous limestones and buff sandy 

 dolomites weathering brown. This description is taken from Logan's 

 notes on the formation near the Canadian boundary. To the south, in 

 the town of Georgia, Franklin County, Vermont, they form a bluish 

 gray dolomitic limestone, followed by a steel-gray dolomitic limestone 

 that passes into a mottled limestone or the Winooski marble. This in 

 turn is subjacent to gray dolomitic limestones in massive layers, some 

 of which are mottled reddish and white, though the larger part are gray 

 and yellow. Still higher up the reddish pink dolomitic limestones ap- 

 pear. There are many variations in the color aud composition of this 

 series between the Canadian border and its point of disappearance 40 

 miles to the south. 



