GEOLOGY OF THE SCHROON LAKE QUADRANGLE 67 



' Calciferous ' was originally applied to the considerable thickness 

 of dolomitic rocks which overlies the Potsdam sandstone in the 

 Champlain and Mohawk valleys. Later on Clarke and Schuchert 

 replaced this by the name Beekmantown, and to the rather unfossili- 

 ferous phase of the formation in the Mohawk valley gave the local 

 name of Little Falls dolomite. . . . Recent work of Ulrich, Rue- 

 demann and Gushing showed that the Little Falls dolomite of the 

 Mohawk valley was the equivalent " of the lower portion of the 

 Champlain Beekmantown, and that it was really separated from 

 the overlying Beekmantown by unconformity and graded through 

 transition beds (Theresa) into the underlying Potsdam sandstone. 



The Schroon Lake and Little Falls dolomitic limestones are 

 almost exactly alike in nearly every way, both being very largely 

 dark-gray, fine-grained, crystalline, usually rather thick bedded, 

 dolomitic, sandy limestones with considerable chert as irregular 

 masses and irregular bunches of crystalline calcite at certain hori- 

 zons, and almost, or entirely, devoid of fossils. Cavities containing 

 very clear quartz crystals, so characteristic of certain horizons 

 of the Little Falls dolomite of the Mohawk valley, were not observed 

 at Schroon Lake, but it is quite possible either that the proper 

 horizons are not there exposed or that such cavities may never 

 have formed there. It is also of interest to note that Potsdam 

 sandstone, the rock with which the Little Falls dolomite is almost 

 .invariably affiliated, outcrops to the southwest of the Schroon 

 Lake dolomite. 



All points considered, then, it is very probable that the Schroon 

 Lake dolomitic limestone should be regarded as Little Falls (Upper 

 Cambrian) dolomite. 



Newly Found Outlier in the Paradox Lake Quadrangle 



During the summer of 1917 the writer discovered an outlier of 

 Paleozoic rock in the Schroon river valley of the Paradox Lake 

 quadrangle 2*^ miles due north of Schroon Falls, or 7 miles north 

 of Schroon Lake village. It lies west of the river and only one- 

 fourth of a mile east of the boundary of the Schroon Lake quad- 

 rangle. In an area of about 2 acres there are exposures of dolo- 

 mite in fairly thick beds resting upon sandstone, a total thickness 

 of not over 25 feet being visible. These strata lie in practically 

 horizontal position. Whether^ trrrs i&Hrtfe Little'"' FaRV dolomite 

 resting upon Potsdam sandstone, 6'fWhe rocks "rep're'sent "transition 

 3 



