32 JOURNAL AND PROCEEDINGS. 



elevation is from 1,500 to 1,600 feet above the present sea level ac- 

 cording to Logan, and probably less than 1,000 feet according to 

 Selwyn. There are many points of 2,500 to 3,000 feet ; in the Ad- 

 irondacks are mountains more than 5,oco feet above the sea; and 

 along the eastern and northern coasts of Labrador are chains esti- 

 mated at heights from 5,000 to 10,000 feet. It is supposed that 

 the denuding forces were not so great or so active in Labrador as 

 farther west ; and having in view the immense extent of the sedi- 

 mentary formations, from at least the base of the Huronian upwards 

 through the Cambrian, Silurian and Devonian systems to the rela- 

 tively recent glacial drift which cover the region of the lakes and be- 

 yond them south and west to a depth in places of many thousands 

 of feet, and the fact that the materials of all these excepting part of 

 the limestones were derived from the ancient rocks of the north, the 

 conclusion appears to be irresistible that the range or ranges, for 

 probably there were several parallel ones, must have reached a lofty 

 height throughout their whole extent. Logan, about forty years 

 ago, gave to this primitive nucleus of the continent the name Lau- 

 rentian, from the rocks which compose it forming the high moun- 

 tainous country known as the Laurentides, which extend for nearly 

 a thousand miles north of the river St. Lawrence from Quebec into 

 Labrador. He maintained that the rocks of the Laurentian system 

 are almost without exception old sedimentary beds which by action 

 of heat have become highly crystalline, composed of schists, fel- 

 spars, quartzites and limestones, with intrusive masses of granites, 

 syenites and diorites, and that their aggregate thickness is not less 

 than 30,000 feet. It seems probable however that a number of the 

 rocks which Logan has described as stratified are of purely igneous 

 origin, and that their foliated structure is a result of folding and 

 shearing when under great pressure they were being raised into 

 mountain forms. The fine-grained hornblende-gneisses, the mica- 

 gneisses and the chlorite-gneisses are of this class, and are often 

 traced into massive granites and granitoid gneisses, which are clearly 

 igneous. "All of these rocks," Van Hise says, "are completely 

 crystalline. None of them show any unmistakeable evidence of 

 having been derived from the sedimentaries, but many can be traced 

 with gradations into massive rocks, and therefore the greater pro- 

 portion of them are igneous, if a completely massive granular struc- 



