400 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [JunC 16, 



undermined it. The removal of the gypsum had exposed, on the 

 northern side of the quarry, some bands of flaggy bituminous lime- 

 stone, nearly in a vertical position. These I found to contain abun- 

 dance of flattened specimens of Conularia quadrisulcata, which 

 occurs also in the gypsiferous rocks at Windsor and at Cape Breton. 

 These fossils mark distinctly the true age of this great mass of 

 gypsum, which, from its isolated position and singular structure, 

 could not be accurately determined on stratigraphical grounds. From 

 the appearance of this mass of gypsum in its present state, I have no 

 doubt that it consists of thick parallel laminae, or thin beds, contorted 

 in an extraordinary manner and closely cemented together. In the 

 highest part of the cliif these bent laminae assume the form of a huge 

 cylinder, incomplete only on its lower side. 



I was informed that, since my last visit, the sandstone cliff of 

 Eagle's Nest, opposite the *'Big Rock," had slipped into the river, 

 leaving a clean face of rock somewhat lower than the former cliff. 



I may also mention that the high cliff at Two Islands, on the op- 

 posite side of the Bay, of which a section is given in my paper on the 

 New Red Sandstone *, has fallen, burying the most interesting part 

 of the section under the mass of trappean debris, which will not for 

 several years be removed by the tides of the Bay. 



7. On the Geology of the Lake of the "Woods, South 

 Hudson's Bay. By Dr. J. J. Bigsby, F.G.S. 



[Plate XXII.] 



In the following pages it is intended to describe the nature, position, 

 and relations of the rock-formations of the Lake of the Woods in 

 South Hudson's Bay, comprising a part of the commercial route 

 from Canada to Rupert's Land, and the eastern terminus of the 

 Boundary-line between the Possessions of Great Britain and the 

 United States, where it passes along the 49th parallel of latitude from 

 hence to the Rocky Mountains. 



This lake is not without its claims to the attention of the Geolo- 

 gical Society. 



It is here that the igneous and metamorphic rocks, which over- 

 spread the half-drowned wildernesses of East Hudson's Bay, have 

 their western termination (for this latitude) ; — here they sink out of 

 sight and are replaced westwards by sedimentary rocks. 



By an examination of the first-mentioned classes of rock in this 

 lake, we learn that they are generally conformable to the great body 

 of crystalline strata which extend from hence 700 miles southwards, 

 — to the River Mississippi in lat. 43°. This great breadth of rocks 

 has a general strike to the W.S.W. 



The Lake of the Woods is 400 miles round by canoe-route, and is 

 7^ miles in extreme length and breadth. Its shape, which is very 



* Quart. Journ. Geol. Soc. vol. iv. p. 50, pi, 5. 



