GEOLOGICAL SURVEY OF THE TERRITORIES. 203 



islied raiu-fall theoretically consequent upon the largely-increased cou- 

 siimption of timber in the building and since the completion of the 

 Pacific Eailroad. On the other hand, upon the same theory, we may 

 refer the previous rise to the results of cultivation of land and planting 

 of trees, and may expect that, as these increase, the lake will again 

 begin to rise and to spread over larger areas. 



As we pass down from the Malade divide into Marsh Valley, the 

 Quebec Group limestone and underlying (Potsdam ?) quartzite outcrop 

 on our right, until the valley spreads, and they disappear beneath 

 the level of the lower terrace. These terraces are very strongly marked 

 through the whole length of this valley ; and an upper one is readily 

 identified, though not so prominent, at the level of about 1,000 feet 

 above the stream. They are on too large a scale, and the valley is too 

 wide, to have resulted from merely the drainage of the small area of 

 mountains about the head of the stream; and I am strongly of the 

 opinion that this must have been at one time the channel for a large out- 

 flow from the Great BavSin. 



Eain caused us a day's delay at Watson's ranch, (formerly Carpen- 

 ter's.) but on the next day (July 1) we moved onward, though showers 

 still continued. At Watson's, a road turns off to the upper caQon of 

 the Port Neuf,* through which it passes to the head- waters of that 

 stream, where it meets the Soda Springs road, and then crosses the 

 divide to Fort Hall. We had proposed to follow this, but found that 

 the river was still high and the fords bad, so that we decided to con- 

 tinue on the stage-road. The distances by the two routes are almost 

 identical. 



The face of the high terrace at Watson's consists of Quebec Group 

 limestone, partly quite cherty, with abundant characteristic fossils, 

 though mostly in fragmentary condition. This is overlaid by heavy 

 beds of white quartzite, followed by Carboniferous limestones. The dips 

 are all easterly, varying from 20^ to 40<^. 



A short distance above the junction of Marsh Creek with the Port 

 jSTeuf, we met with the tirst appearance of the basalt-rock which fills the 

 Great Snake River Basin. It makes its first appearance as a narrow 

 stream, which forms the floor of the upper canon of the Port Neuf 

 through its whole length, having had its source in one of the old craters 

 still standing near Soda Springs, though their fires have long been 

 extinct. A short distance up the stream from the point where the 

 stage-road strikes it, we found the lowest of a long series of calcareous 

 spring-deposits, which form a prominent feature of the caiion for several 

 miles, damming the stream at numerous points, so as to make small but 

 pretty waterfalls. This lower dam is about 20 feet high, but with a per- 

 pendicular fiill of only about 12 feet. In the caiion, the river is some- 

 times one side of the basalt and sometimes on the other. Where it 

 strikes the wider level of the continuation of Marsh Valley, it has basalt 

 on both sides at first, but soon passes to the right, where it has dug out 

 a channel in the upturned edges of the bordering limestones, leaving the 

 basalt as a perpendicular barrier on the left, which rapidly increases in 

 'height as the stream descends. The surface of the basalt has, of course, 

 some slope, corresponding with that of the valley at the time of the 

 volcanic outflow; but it is here much more moderate than that of the 

 present stream, which rushes ajong rapidly, with occasional leaps of a 

 lew feet. The foot and face of the hill on the east side of the valley con- 

 sist of mostly thin-bedded limestones of the Quebec Group, dipping 



* So uamed after an old French-Canadian trapper. 



