STATE GEOLOGIST. 141 



I. LOWER SILURIAN SYSTEM. 



3. Hudson River Group, (observed,) 18 feet: 



Argillaceous limestone, filled with fossils in the upper 



part, 15 feet: N. side Drummond's Island. 

 Bluish-gray subcrystalline limestone, (observed,) 3 feet. 

 2. Trenton Group, 32 feet: 

 (e) Dark blue, subcrystalline limestone, with 3 feet of dark- 

 green areno-calcareous shale above, 7 feet; North side 

 Drummond's and St. Joseph's Islands, 

 (d) Dull-gray limestone, hard, silicious, 2 feet. Ibid, 

 (c) Blue, argillaceous limestone, 9 feet: Ibid. 

 (6) Limestone, dark, bluish-gray, with partings of green 



shale, 12 feet: Ibid. 

 (a) Limeslone, gray, silicious, resting on quartz, 2 feet: Sul- 

 phur Island, north of Drummond's. 



1. Lake Superior Sandstone, (Potsdam), at the Sault, 18 feet. 



Total observed thickness of the Paleozoic rocks, 1,725 feet.. 

 Actual thickness probably 2,500 feet. 



