206 New York State Museum 



about 50,000 feet is limestone. This calcareous phase is 

 restricted to southern Ontario, the Adirondacks in New 

 York State and Quebec, but the Grenville series is also 

 found in the Thousand Islands, probably in the High- 

 lands-of-the-Hudson, southern Baffin Land and covering 

 much of Labrador. In this series the crystalline lime- 

 stones alternate with quartzites which are altered sand- 

 stones. There are also interbedded gneisses and schists 

 formed partly from the intruded igneous rocks and 

 partly from the sediments in contact with these intru- 

 sives. The Grenville strata have been so greatly changed 

 that certain of the sedimentary characters have been 

 obliterated, but among the proofs of their sedimentary 

 origin is the common occurrence of the rocks in alternat- 

 ing layers, sharply contrasted in composition and color 

 and indicating a difference in the original sediments. The 

 extensive beds of crystalline limestone and beds of almost 

 pure quartz rocks also indicate sedimentary origin, as well 

 as the flakes of graphite, derived from carbon of organic 

 origin (primitive marine plants) so common throughout 

 the formation. Graphite is so abundant in the beds of 

 Essex and Saratoga counties that it has been very exten- 

 sively mined as a mineral. 



The Adirondacks also are noted for their rich iron ores 

 (magnetite and hematite) which have been extensively 

 worked along the east and in the northwest and northern 

 areas. Large bodies of magnetite in the central Adiron- 

 dacks remain undeveloped. These deposits are somewhat 

 remote from railroads but the resources of the district 

 are probably the greatest in the Adirondack region. 



The fact that the Grenville series is found in northern 

 (Adirondacks) and southeastern (Highlands-of-the-Hud- 

 son) New York, along the western border of New Eng- 

 land and in the Province of Ontario, north of Lake On- 



