232 Tertiary. 



or else the precipitous character of the side of the valley: has altogether 

 prevented their formation. The steps vary greatly in height, the 

 greatest height observed being as much as one hundred feet ; in width, 

 from one to five chains is not uncommon. 



Nearly all the lakes in British Columbia occupy long, narrow de- 

 pressions in the river valleys, and are, in fact, lake-like expansions of 

 the livers. There is no doubt that such lakes were at one time much 

 more extended and more numerous than they now are ; and that, in 

 many places, as, for instance, at L}- ttou, and on the north bend of the 

 Thompson, and at Canoe river crossing, the terraces mark the old 

 margins of these lakes, while in others they doubtless represent only 

 the ordinary flood-flats of the rivers. The removal of the rocky bar- 

 riers by which these inland waters were confined would result in the 

 formation of such gorges and canons as we now find_ on the Fraser at 

 Gale, and below Ljtton, as well as on the North Thompson at Murchi- 

 son's Rapids, and on Canoe river below the wide flats at the crossing, 

 and would, without any general movement of elevation, drain off the 

 waters of the lakes, leaving the old shore lines exactly as we now see 

 them, at corresponding heights on both sides of the valle^^s. Ordinary 

 alluvial river flats do not commonly occur in that manner, but where 

 a flat occurs on one side there is usually a steep bank on the other, 

 and especially is this so along rapid rivers which traverse a mountain- 

 ous country. 



Dr. F. V. Hayden* said, that Fort Bridger is located in what appears 

 to the eye a sort of basin, inclosed by high, arid table lands, but really 

 in a central portion of the drainage of Black's Fork. The beautiful 

 valleys, Smith's, Black's, and Muddy, have been carved out of the 

 horizontal strata, and between the streams are terraces and flat table 

 lands, which give a singular outline to the surface of the country. 

 No forces now in operation, in this vicinity, could have given the ex- 

 isting features to the surface of the country, and the cause must have 

 been local, proceeding from the northern slope of the Uintas. The 

 beautiful table-top divides between the vallej^s, and streams are exten- 

 sions into the plains of the radiating ridges of the mountain slope, and 

 are literally paved, in many places, with the water-worn bowlders 

 of the purplish sandstones and quartzites, and with the carbon- 

 iferous limestones that compose the nucleus of the Uinta range. Here 

 and there we can see a flat-topped butte cut ofi" by erosion from some 

 of the intervening ridges, and rising above the surrounding country as 



* U. S. Geo. Sur. of Wyoming. 



