GEOLOGY OF THE BROADALBIN QUADRANGLE 1 3 



in small masses have been encountered, as e. g. one and one-half 

 miles west and two and one-half miles northwest of Edinburg, but, 

 on the whole, the rocks are decidedly Grenville and have been so 

 mapped. For the most part they are f eldspar-quartz-biotite-garnet 

 gneisses with occasional hornblende or sillimanite gneisses. The 

 strike is generally northeast and dip from 20 to 40° south. 



Two small outcrops of the quartzite may be seen along Butler 

 creek (below the falls) at Edinburg where the creek has just cut 

 through the Potsdam, but they are too small to be shown on the 

 geologic map. 



North of Northville the small area shows chiefly feldspar-quartz- 

 garnet-gneisses with a distinct belt of pure quartzite along the 

 northern border. These rocks strike east- west and dip 45° south. 



The Grenville area southwest of Sacandaga Park is character- 

 ized chiefly by feldspar-quartz-biotite-garnet gneisses and schists. 

 Toward the west these rocks are rather massive looking, dark gray 

 and rich in hornblende; while toward the northeast and south 'they 

 are clearly banded, contain sillimanite and lack hornblende, and 

 frequently have in them small outcrops of granitic and syenitic 

 rocks. The strikes and dips of this area are very variable. 



In the area west of Cranberry Creek the rocks are, toward the 

 north, mostly thin bedded, very schistose, granulated, and severely 

 dynamically metamorphosed. Toward the south, in the Precambric 

 tongue, they are mostly thin-bedded feldspar-quartz-garnet gneisses, 

 at times associated with small masses of good porphyritic syenite 

 or granite. Throughout this area the strike is fairly constant north 

 40° east, dip 30° south. 



Stratigraphy and thickness of the Grenville. Prom the above 

 it is evident that the great bulk of original Grenville sediments were 

 shales, often sandy and carbonaceous, and that these were asso- 

 ciated with smaller amounts of pretty pure sandstone and impure 

 limestone. It was hoped that the largest Grenville area might fur- 

 nish some clew to the stratigraphy of these ancient sediments and, 

 although no conclusive results have been obtained, some suggestive 

 observations have been made. From a point three-quarters of a 

 mile north-northeast of Batchellerville to a point one and one-half 

 miles southeast of Fox Hill is four miles and the line connecting 

 these points passes, at right angles to the strike, over an apparently 

 regular succession of Grenville strata. The dip of the beds is 

 from 20° to 30° to the southeast. Taking the average dip 

 as 25° the thickness of the Grenville in this partial section 

 would be nearly 10,000 feet which is very small compared with re- 



