THE DATE OF THE GLACIAL PERIOD. 569 



"There is also much evidence that erosion has been trifling 

 since the commencement of glaciation, excepting under 

 peculiar circumstances, east of the range, for example, at 

 Virginia City; and sites which there is every reason to sup- 

 pose preglacial have scarcely suffered at all from erosion, 

 so that depressions down which water runs at every shower 

 are not yet marked with water-courses, while older rocks, 

 even of tertiary age and close by, are deeply carved. The 

 rainfall at Virginia City is, to be sure, only about ten inches, 

 so that rock would erode only say one-third as fast as on the 

 California coast; but even when full allowance is made for 

 this difference, it is clear that these andesites must be much 

 younger than the commencement of glaciation in the north- 

 eastern portion of the continent as usually estimated. So, 

 too, the andesites near Clear Lake, in California, though 

 beyond a doubt preglacial, have suffered little erosion, and 

 one of the masses, Mount Konocti (or Uncle Sam), has 

 nearly as characteristic a volcanic form as Mount Vesuvius."* 



Dr. Bellf also writes as follows: "On Portland promontory, 

 on the east coast of Hudson's Bay, in latitude 58°, and south- 

 ward, the high, rocky hills are completely glaciated and bare. 

 The stria are as fresh looking as if the ice had left them 

 only yesterday. When the sun bursts upon these hills 

 after they have been wet by the rain, they glitter and shine 

 like the tinned roofs of the city of Montreal." Again, Pro- 

 fessor MacounJ writes of the red Laurentian gneiss in the 

 vicinity of Fort Chippewayan, at the west end of Lake Atha- 

 basca: "The rocks around the fort are all smoothed and 

 polished by ice action. When the sun shines they glisten 

 like so much glass, and a person walking upon them is in 

 constant danger of f ailing/ ' 



* "Bulletin of the Geological Society of America," vol. ii, pp. 

 196, 197. To the same effect see the testimony of Prof. I. C. Russell 

 and Prof. Gilbert, below p. 609. 



f "Bulletin of the Geological Society of America," vol. i, p. 308. 



X "Geological Survey of Canada, Report of Progress," 1875-1876, 

 p. 90. 



