272 Tertiary. 



miles, near Agate lakes, north of the Sweetwater. All of them are 

 water- worn. It is an accepted fact that the "moss" in agates is but 

 the result of impeded crystallization. The best exposures of the Plio- 

 ocene series are low down on the Sweetwater, and along the northern 

 edge of the plateau. The thickness is estimated at from 700 to 900 

 feet. 



The Wyoming Conglomerate is structureless, and composed of the 

 most varying material. It is the product of all formations existing 

 within a given area. Along the entire northern slope of the Sweet- 

 water and Seminole hills there are enormous deposits of it. The thick- 

 ness is estimated at from 10 to 400 feet. It is also abundant along the 

 southern slope of the Sweetwater mountains, in the Pliocene valley 

 west of South Pass, and is scattered to a greater or less extent all over 

 the country, which has been subjected to extensive erosion. The 

 maximum accumulation occurs along the shores of the former Ter- 

 tiary lakes, and was probably carried there by the waters draining in- 

 to them, and it is, therefore, of the age of the younger Pliocene marls 

 and shales. 



George M. Dawson* said that in the plateau region in the southern 

 part of British Columbia, lying east of the Coast Ranges, terraces are 

 exhibited on a scale scarcely equaled elsewhere. They border the 

 river valleys, are found attached to the flanks of the mountains to a 

 great height, though none have been found in this region equal to the 

 elevation of that on Ilgachuz mountain in the north — 5,270 feet. The 

 higher terraces can be due to nothing else than a general submergence 

 of the country. Five of the best marked terraces on the southern 

 slope of Iron mountain, at the mouth of the Cold water, have the follow- 

 ing elevations above the sea, viz: 2,386, 3,063,3,392, 3,611, and 3,715 feet. 

 The last mentioned is. the highest observed, and is quite narrow. 

 Above this, the drift covering becomes thinner, but rolled stones, some 

 of them certainly from a distance, occur to the very summit — 5,280 

 feet above the sea. The elevation of the white silt terrace bordering 

 Okauagan lake, is 200 feet above the lake, or 1.277 feet abova the sea. 

 Leaving this to ascend the Okanagan mountain, south of the Mission, 

 a great series of high terraces is passed ovei'. The heights of six of 

 these areas follows: 1,862, 2,042, 2,141, 2,645, 2,800, and 2,839 feet. 

 On the northern slope of the same mountain, six principal terraces 

 have the following heights: 1,451, 1,579, 1,962, 2,452, 2,553, and 2,879 

 feet. 



* Geo. Sur. of Canada. 



