﻿440 



PROCEEDINGS OE THE GEOLOGICAL SOCIETY. 



[Apr. 10. 



very hard, and having an angular fracture. At Stony Hill, about fif- 

 teen miles north-west from the upper fort, there is an isolated bluff 

 of limestone rising from the plain-level to the height of 80 feet. 

 The south and western exposures are abrupt and waterworn, it 

 having evidently been at one time an island ; and indeed during the 

 great floods which have several times inundated the settlement it 

 has been one of the few spots upon which the inhabitants can take 

 refuge, reaching it by means of boats. The beds of limestone are 

 horizontal or nearly so, and are slightly diffei-ent from those at Port 

 Garry in their mineral aspect, having a more crystalline structure 

 and the colour being of a reddish hue. No fossils can be discovered 

 in newly fractured portions, but on the weathered surfaces a few 

 obscure remains of fossils are to be seen projecting, together with 

 siliceous and gritty particles, from a dull floury surface. 



The Silurian rocks have now been traced continuously from Lake 

 Superior west of the sources of the Mississippi, and thence into the 

 valley of Lake Winnipeg and on to the Arctic Ocean, skirting the 

 more ancient axis. On the shore of Lake Winnipeg they bave been 

 observed much disturbed and even vertical by Dr. Owen (' Report on 

 (Jeol. of Minesota,' &c), but in general they rest nearly horizontally, 

 or with only a very slight dip. 



Resting on the Silurian strata, Mr. Hind has detected limestone 

 with Devonian fossils in a tract to the west of Lake Winnipeg, where 

 there are copious salt-springs, the brine from which is used for the 

 manufacture of salt. He considers the line marked by the occur- 

 rence of these salt-springs to indicate the outcrop of the Devonian 

 strata. 



The route of the Expedition at once passed from Silurian to Cre- 

 taceous rocks without any indications of the intervening formations 

 until reaching the Rocky Mountains. 



STRUCTURE OP THE ROCKY MOUNTAINS. 



P/n/sical Character. — The plains at the eastern base of the Rocky 

 Mountains are, as I have before stated, elevated above the sea 4000 

 feet ; and, as the average limit of vigorous vegetation in that latitude 

 is attained at 5000 to 6000 feet, the greater mass of the mountains 

 displays in consequence naked and bald surfaces, which are generally 

 very precipitous. Their structure is thus easily discerned to be of 

 strata the real thickness of which, originally very great, has been 

 much exaggerated by the complex flexures which cause the beds to 

 recur again and again, sometimes even in the same mountain. The 

 apparent confusion is so great from this cause as to strike the eye 

 at once, and it is not until observations have been made over a con- 

 siderable extent of the range that the extreme regularity with which 

 the disturbing agencies have been exercised becomes evident. The 

 flexures of the strata on the eastern part of the mountains have 

 been so completely inverted that the prevailing dip is towards the 

 centre of the mountains — that is. to the W. and S. The strike of the 

 plications varies, but in a regular manner. From Bow Fort, south- 

 wards, it is only a few degrees east of south ; but north of that river 



