MEASUKEMENTS OF POSTGLACIAL TIME. 239 



deposition of nioditied di'ift iu the Connecticut Valley at Northamptou. 

 Mass., from which he believes that not more than ten thousand years have 

 elapsed since the Ice age. 



flaking such inquiry also concerning the glaciation of Europe, we 

 find that in Wales and in Yorkshire, England, tlie amount of denudation of 

 limestone rocks on which bowlders lie has been regarded by ]\Ir. D. Mack- 

 intosh as proof that a period of not more than six thousand years has 

 elapsed since the bowlders were left in their positions.^ The vertical 

 extent of this denudation, averaging about 6 inches, is nearly the same 

 with that observed in the southwest part of the Province of Quebec by Su* 

 William Logan and Dr. Robert Bell, where veins of quartz marked with 

 glacial striae stand out to various heights not exceeding 1 foot above the 

 weathered surface of the inclosing limestone." 



Another indication that the final melting of the ice-sheet upon British 

 America was separated by only a very short interval, geologically speak- 

 ing, from the present time is seen in the wonderfully perfect preservation 

 of the glacial striation and polishing on the surfaces of the more enduring- 

 rocks. Of their character in one noteworthy district Dr. Bell writes as 

 follows: "On Port-land promontory, on the east coast of Hudson's Bay, in 

 latitude 58°, and southward, the hig'h, rocky hills are completely glaciated 

 and bare. The strise are as fresh-looking as if the ice had left them only 

 yesterday. When the sun bursts vipon these hills after they have been 

 wet by the rain, they glitter and shine like the tinned roofs of the city of 

 Montreal."^ Again, Professor jMacoun writes of the red Laurentian gneiss 

 in the vicinity of Fort Chipewyan, at the west end of Lake Athabasca: 

 "The rocks ai'ound the fort are all smoothed and polished l)y ice action. 

 When the sun shines they glisten like so much glass, and a person walking 

 upon them is in constant danger of falling."* It seems impossible that 

 these rock exposures can have so well withstood weathering in the severe 

 climate of those northern regions longer than a few thousand years at the 



' Quart. Jour. Geol. Soc, Vol. XXXIX, 1883, iu Proceedings, pp. 67-69. Compare id., Vol. XLII, 

 1886, pp. 527-539. 



'Bulletin, G. S. A., Vol. I, 1889, p. 306. 



3 Bulletin, G. S. A.. Vc.I. I, p. :W8. 



■• Geol. Survey of Canada, Report of Progress, 1875-76, p. 90. 



