GEOLOGICAL FORMATIONS 335 



Age Lithological characters 



Mesozoie Chiefly slates, phyllites, quartzites, sandstones, 



(Probably largely Cretaceous) shales, dolomites, and magnesites. 

 Carboniferous Chiefly limestones, cherts, and cherty conglom- 

 erates. 

 Ordovician-Silurinn Limestones and dolomites. 



The Ordovician-Siluriaii limestones and dolomites constitute the bed- 

 rock of the northern 20 miles of the area under consideration. These 

 beds have an aggregate thickness of at least 5,000 feet and range from 



FiGLKE 1. — Mai) of Yukon oikI Aluska 



Showing the area along the Yukon-Alaska boundary (141st meridian) : whicli was geo- 

 logically mapped and studied during 1911, by D. D. Cairnes. for the Canadian Geological 

 Survey. 



white through various shades of grey to almost black, and are even occa- 

 sionally decidedly reddish or pink in color. These rocks are considerably 

 folded, distorted, and metamorphosed, and are characteristically massive 

 and crystalline in structure; but particularly in some of tlic darker 

 members the bedding planes are in places still quite apparent. Fossils 

 have been collected from these beds in several localities aiul have all been 

 identified as being either of Ordovician or Silurian age. 



