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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Apr. 10, 



are of much more recent formation, having been derived from the 

 deposits along the base of the mountains *. 



This may not only be inferred from their relative position, but also 

 from the composition of the terraces themselves ; for, although the 

 pebbles are the same in all, those in the valley-terraces are well 

 cleaned and mixed with sand, while in the terraces along the moun- 

 tains and on the Cypres Hills they are often encrusted with white 

 calcareous matter. This sometimes increases so as to form a perfect 

 cement, so hard as to allow of the fracture of the pebbles before that 

 of the matrix, just as is seen in some ancient conglomerates f. 



On approaching the Eocky Mountains the extreme regularity with 

 which these deposits have been terraced by retiring waters at once 

 attracts attention. At the place where Belly Biver leaves the moun- 

 tains, in latitude 49° 34' N., Capt. Blakiston measured three of these 

 terraces, and found that they were elevated 61, 152, and 202 feet 

 above the river-level, which at that point, according to his measure- 

 ment, is 4024 feet above the sea. He describes them as being " very 

 marked, appearing as a succession of steps from the level of the river 

 to the plain above, often in sight for miles and running horizontally. 

 The tread of the step is of variable width, but the rise is nearly 

 always abrupt and well marked." From the regularity of these 

 enibanknient-like terraces in the valley of one river, he named it 

 Railway River (Further Papers, Pallisor's Expedition, 1860, p. 68). 



On Bow Biver they are also well marked, and there I measured 

 four at the altitudes above the river-level of 30, 140, 170, and 240 

 feet, and traces of one still higher at 350 feet. The valley of Bow 

 Biver within the mountains is narrow and tortuous for the first 

 twelve miles, and in this part of its course the terraces are hardly 

 preserved. Above this point, where it occupies one of the expanded 

 horizontal valleys conforming to the strike of the strata, they are 

 again enormously developed. Even on gaining the Vermilion Pass 

 the only steep climb is at first, up the face of these terraces for 150 

 feet ; and then a gentle slope leads to the height of land. 



The valley of the North Saskatchewan is much wider and more 

 direct within the Eocky Mountains ; and there we have not only 

 these terraces remarkably developed, but also their mineral compo- 

 sition much altered, partaking of what will be found to be their 

 character on the western slope of the mountains. At a similar 

 place, with respect to the mountains, to where the terraces were 

 measured on Bow River, four were estimated to have an altitude of 

 25, 70, 180, and 300 feet above the North Saskatchewan. The 

 shingle, cemented into a hard conglomerate, was here seen to rest 

 on the edges of the contorted strata of grit and shale with thin 



* In latitude 42 D at the base of the Eocky Mountains near Fort Laramie, 

 Havdeii describes similar " deposits of coarse conglomerate, 50 to 150 feet in 

 thickness, formed since the scooping out of the present river-valleys." — Proc. 

 Acad. Nat Sci. 1858. 



t Darwin says of the slungle-formation of Patagonia, " The pebbles are im- 

 bedded in a white, gritty, calcareous matrix very like mortar, sometimes merely 

 covering with a whitewash the separate stones, and sometimes forming the greater 

 part of the mass." — Gcol. of S. America, p. 19. 



