GEOLOGIC FORMATIONS OF NEW YORK 141 



The principal group of 'mountains, which includes Mt Marcy, is 

 of massive rocks known as norite and anorthosite. The pre- 

 vailing rocks of the wilderness are, however, gneisses of different 

 kinds. In these are many local intrusions of granite and other 

 eruptives. Trap, serpentine and many other rocks of igneous 

 origin are found in all parts of the district. The great route of 

 travel through Lakes George and Champlain is bordered by 

 mountains and cliffs, in which these rocks are seen in great 

 variety. 



In the Mohawk valley are small exposures of pre-Cambrian, at 

 Littlefalls and near Spraker's. These are important localities 

 and show the relations of 'the over-lying Palaeozoic rocks. 



Proterozoic or Agnotozoic 



Eocks of this age are not definitely known in New York. They 

 are well represented in the Lake Superior region by those forma- 

 tions known as Huronian and the copper bearing deposits of the 

 Keeweenaw peninsula. West of the Rocky mountains, they are 

 developed extensively. All rocks between the Archaean and the 

 Cambrian are included. 



Palaeozoic 



Upon the plutonic and metamorphic rocks of the Archaean 

 in New York rest directly the Palaeozoic strata which are all 

 fossil-bearing rocks. The Palaeozoic series includes all strata 

 from the base of the Cambrian to the summit of the Carbonif- 

 erous. 



These stratified fossil-bearing rocks form the greater part of 

 the state of New York. 



At the beginning of the Palaeozoic, all life was marine, prob- 

 ably because the land surfaces were at first too small to materi- 

 ally influence the evolution of living forms. In the Cambrian, 

 crustaceans prevailed, in the Lower Silurian the Cephalopods or 

 cuttle fishes, in the Devonian the soft boned fishes were the 

 dominant type, while in the Carboniferous, fishes and amphibians 

 divided the honors of the sea and the land. 



