GEOLOGICAL SUEVEY OF THE TEEEITOEIES. 27 



CHAPTER II. 



FEOM FOET HALL, IDAHO, TO FOET ELLIS, MONTANA. 



We will not take our leave of Fort Hall without a word of thanks to 

 the ofi&cers of that post for their hospitable courtesy to us. We remained 

 in this beautiful locality, a real oasis it might be called, two days, rest- 

 ing our animals and laying in supplies and making repairs. Every 

 facility that could possibly be provided for us, was granted by Captain 

 J. E. Putnam, the officer in command, as well as by Lieutenant Wilson, 

 commissary and quartermaster. The manner in which Captain Putnam 

 extended the courtesies of the post to all my party was even more 

 grateful than the material afforded. The assistance we obtained here 

 advanced our explorations several days of time. Fort Hall is a small 

 but exceedingly neat post, which was constructed by the officer at pres- 

 ent in command about one year ago, and is located in a beautiful, fer- 

 tile, grassy valley, among the foot-hills on the east side of the Snake 

 Eiver Basin, about forty miles east of the old Fort Hall. Numerous 

 streams of pure water have been conveyed, by artificial channels, all 

 through and around the grounds, so that, in the dry season, when the 

 vegetation of the surrounding country is parched by the sun's rays, it is 

 here as fresh and green as in spring-time. During the winter, the waters 

 coming from Warm Springs, about two miles above the post, aever 

 freeze over, and the whole valley is protected from the cold winds by 

 the surrounding hills, so that I do not hesitate to regard it as one of the 

 most desirable spots in Idaho. 'No finer locality for a military post 

 could have been selected in this region. 



In the afternoon of June 23, we left this pleasant resting-place and the 

 kind hospitality of its officers with reluctance, and made our camp on 

 Blackfoot Fork, about seven miles to the northward. This is a pretty 

 stream about 30 feet wide, and 6 to 8 feet deep, taking its rise near Soda 

 Springs, and draining a large area. All through the valleys of the main 

 stream and its branches, are this results of the basaltic overflow, and in 

 its passage through the mountains it has carved out a deep caiion 

 through basalts, limestones, and quartzites. After leaving the moun- 

 tains it flows across the plains with a swift current, about thirty miles^ 

 over a floor of basalt, to the Snake Eiver. From Fort Hall the road 

 winds among low hills, underlaid by the light-gray marls and sands of 

 the Pliocene, with some quite high ridges or hills of blown sand. In 

 some instances the loose sand is so deep as to impede traveling. The 

 bottoms of Blackfoot Creek are quite sandy, and the vast quantities of 

 fresh-water shells scattered about formed a noticeable feature, and indi- 

 cated an excess of molluscous life. 



On the morning of the 24th I followed up the south side of Blackfoot 

 Creek to the mouth of the caiion. The lower hills are covered with 

 igneous rocks. The higher ridges have a trend about northwest and 

 south-east, and appear to form irregular anticlinals. Sometimes a cap of 

 basalt will lap, roof-like, on to the ends of these ridges as they extend 

 down to the plains. This bed of basalt inclines more or less, on the sides 

 of the ridges, but gradually becomes horizontal in the plains. A careful 

 examination of one of the ridges showed it to be composed of quartzites, 

 inclining northeast at a high angle, with the external somber steel-gray 

 hue that strata of all ages seem to have when affected by contact with 

 the igneous rocks in their outflow. Over the quartzites, and conform- 

 ing to them, are strata of Carboniferous limestones. At the point where 



