210 New York State Museum 



of the Adirondacks and Canada, which form a series 

 of ridges, chiefly on the east side of the Hudson, north 

 as far as the Highlands proper. Above the Fordham 

 gneiss is a series of sedimentary formations, the Low- 

 err -e-Inwood-M anhattan series consisting of the Low- 

 erre quartzite, Inwood limestone and Manhattan schist. 

 This series has at various times been regarded as of 

 Precambrian, Cambrian or Cambro-Ordovician age 

 but the most recent investigations indicate a Precam- 

 brian age and the rocks are regarded as belonging to late 

 Grenville time. Igneous intrusions, such as those found 

 in the Adirondacks are also known in the Highlands-of- 

 the-Hudson, though over much of the Precambrian 

 area, especially in Orange and Rockland counties, these 

 igneous rocks have not been differentiated from the 

 gneisses of sedimentary origin. These intrusives include 

 the Storm King granite and granites of similar types in 

 adjacent areas. There are later igneous intrusions in the 

 form of dikes, bosses and lenses which are frequent over 

 much of this area. Excellent iron ore is very abundant 

 in this Precambrian area, particularly in Orange and 

 Putnam counties where the ore is magnetite, and has been 

 extensively worked. 



Literature 

 For the general discussion of the Precambrian eras 

 the student is referred to any of the textbooks of his- 

 torical geology as Chamberlin and Mac Clintock ('30), 

 Chamberlin and Salisbury ("09, '30), Cleland ('16, 

 '30), Coleman and Parks ('22), Grabau ('20), 

 Schuchert ('24), Scott ('24) and to Schuchert and 

 LeVene ('27). For climates, besides the textbooks may 

 be added Schuchert ('14). A very full but technical 

 treatment of the Precambrian of North America may 



