GEOLOGICAL SURVEY OF THE TEEEITOEIES. 25 



tnre is well shown where the river has cut through the basalt, revealing 

 150' feet in thickness, with the floor or terraces; the lower one is the im- 

 mediate channel of the river, and the other forming distinct walls ois 

 either side, with an obscure columnar fracture. I am inclined to believe 

 that there were at least two important periods of overflow of basalt all _ 

 over this region, although in a geological sense they are connected to-' 

 gether. After leaving Port E^euf Oaiion we come out into the broad i^lains 

 bordering on Snake Eiver; on either side, as we continue northward to 

 Eoss's Fork, we find the hills of various heights and comi)osed of a va- 

 riety of quartziteSjWith some limestones. They are much rounded, and 

 covered with a heavy deposit of debris or kind of drift, and the whitish 

 and gray sandstones and the yellow and drab marl of the Pliocene fill 

 up the irregularities of the surface, and sometimes incline at a small 

 angle, as if they had participated in some of the later movements that 

 elevated the country to its present position. From the stage station on 

 Eoss's Fork to the present location of Fort Hall is about 16 miles. The 

 valley is a beautiful one^ and was originally called Warm Spring Valley, 

 from some warm springs that form the sources of the little streams that 

 flow through it, but it has since received the patriotic name of Lincoln 

 Valley. Among the lower ranges of hills that border the east side of 

 the great Snake Eiver basin, especially from Port Neuf CaSon north- 

 ward, the Pliocene deposits are well shown, and lie beneath the basaltic 

 floor. In the Port Neuf Canon this fact is illustrated by the wearing away 

 of the cap or floor of basalt in a number of localities, but on the sides 

 of the hills this is shown with equal clearness by the elevations of 

 the basalt. The dip of the beds is not great, usually not more than 5° or 

 10°, and in all cases in the direction of the great basin. This would in- 

 dicate that there had been a moderate elevation of the mountain ranges 

 or a depression of the basin at a very modern date, even approaching very 

 close to our present period. The effusion of such a vast amount of igne- 

 ous matter from the interior of the earth might suggest the possibility, 

 or even ]}robability, that the cause of the subsequent changes in the hills^ 

 around the borders, was either contemporaneous or subsequent to the 

 effusion of the melted material. If the elevation began with the erup- 

 tion, it certainly continued long after it ceased, inasmuch as the basalt 

 is lifted up in thick beds, at the same angle with the underlying strata. 

 ]Srot only in the valley of the Port i^euf and Snake Eiver is the basalt 

 found in conjunction with the lake deposits, but in numerous localities 

 all over the isTorthwest, it seems to rest upon these Pliocene beds, readilj^ 

 adapting itself by the form of the under surface to the irregularities of 

 the surface of the lake deposits. 



A tew Vv'ords in regard to the geological character of the hills border- 

 ing Lincoln Valley, around Fort Hall, may not be without interest in 

 this connection. In ascending a small gorge-like valley east of the fort^ 

 where the waters have excavated a channel directly through the differ- 

 ent beds, we have excellent opportunities for studying such of them as 

 are developed in this region. There is a general dip to the strata that 

 may be regarded as uniform and in one direction, but the local disturb- 

 ances are, oftentimes, very complicated, and in many cases formations 

 which are really well developed are entirely concealed over large areas, 

 or simply crop out here and there over very restricted areas. The moun- 

 tain ranges all over the West are full of canons and valleys, cuts or 

 gashes, from the axes or central portions to the plains. These vary so 

 much in character, owing to the intensity of the erosive force, that some 

 of them may penetrate the very core of the mountain, and cut through 

 all the strata on the sides into the plains, or it may be more or less shal- 



