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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Apr. 10, 



At the soiu'ce of the North Saskatchewan the mountains are very 

 massive, and are principally composed of a deep-blue compact lime- 

 stone, that often contains nodules of iron-pyrites (c, fig. 14). A few- 

 specimens of Atrypa (^reticularis and Athyris lead Mr. Salter to 

 regard these limestones as Devonian. To the west of the great 

 Columbian valley the strata were only seen in descending the Koo- 

 tanie River, as shown in the section , fig. 14. That river breaks through 

 a succession of well-defined ranges that never rise to any great 

 altitude, and are composed of dark schists («'), traversed by quartz - 

 veins, the whole forming beautifully developed flexures. Some 

 miles east of Ladder Lake the slates (e) were again seen underlying 

 these schists, and at that place commences a district of granitic 

 country (/), where mountain-ridges rise as rounded masses to the 

 height of 800 to 1000 feet above the general level. 



Towards Fort Colvile the Kullespellem Mountains bound the 

 Columbia to the east, and are formed of quartzose slates in thin 

 beds, limestone partly altered, and serpentine. At the south end of 

 the Kulespellem Mountains the great trap-floes of the Columbian 

 Plains commence, and are there seen to overlie the granite and other 

 strata, filling up the hollows in their surface. 



The horizontal extent of these lava-floes is truly wonderful, as 

 they occupy nearly the whole surface of the great Columbian Desert 

 without an)- chain of mountains or peaks existing to which their 

 origin can be referred. 



This great plain is frequently cut by chasms 500 to 600 feet deep, 

 the sides of which expose stratum after stratum of thin lavas inter- 

 calated with softer tufaceous beds, the whole being quite horizontal. 

 The lava-floes have often a columnar structure, especially in the 

 neighbourhood of depressions in the plain, such as Sil-kat-kiva Lake, 

 which probably mark the position of ancient craters. At some points 

 up Snake River, American parties have procured Tertiary fossils from 

 the tufaceous limestone that underlies these basalts. 



The whole way to the Dalles the Columbia flows through an 

 enormous chasm in these stratified lavas and tufas, giving rise to 

 most wonderful scenery. Often the whole of this mighty river is 

 compressed between perpendicular walls of basalt, but with a 

 channel of such depth that its treacherously swift current preserves a 

 glassy surface. 



CASCADE KANGE. 



Where the Columbia breaks through the Cascade Range there 

 is a great rapid rather than a fall, from which the moun- 

 tains have derived their name, and connected with the formation 

 of which there is an old Indian legend. The river from the 

 Dalles to this point, a distance of forty miles, is almost without 

 current, and bounded by a perpendicular wall of mountains on cither 

 hand, and the story is, that at one time the river had a uniformly swift 

 current the whole way, and that where the Cascades now are, it 

 then passed under a gigantic natural arch that crossed from side to side 

 of the chasm. During a great earthquake this arch fell down, and 

 now remains as the chain of islands across the head of the Cascades, 



