238 Tertiary. 



the bridge, is 4,542 feet, and the highest terrace on the east side is 

 4,737 feet, and the highest on the west side is 4,779 feet. The imme- 

 diate valley of Bear river may be said to have been worn out of the Plio- 

 cene or lake deposit. 



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

 Great Snake river basin, especially from Port Neuf Canon northward, 

 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, usuall}- nut more than 5° or 

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

 indicate that there had been a moderate elevation of the mountain 

 ranges, or a depression of the basin at a very modern date, even ap- 

 proaching very close to our present period. The effusion of such a vast 

 amount of igneous matter from the interior of the earth, might suggest 

 the possibility, or even probability, 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 eruption, it certainly continued long after it ceased, in- 

 asmuch as the basalt is lifted up in thick beds, at the same angle with 

 the underl^ang strata. Not only in the valley of the Port Neuf and 

 Snake river is the basalt found in conjunction with lake deposits, but 

 in numerous localities all over the northwest, it seems to rest upon these 

 Pliocene beds, readil}' adapting itself b}' the form of the under surface 

 to the irregularities of the surface of the lake deposits. 



Prof. Eug. W. Hilgard* divided the Eocene of Alabama and Missis- 

 sippi in descending order, into, 1st, Vicksburg Group, 120 feet; 2d, 

 Red Bluff Group, 12 feet; 3d, Jackson Group, 80 feet; 4th, Claiborne 

 Group, 60 feet; 5th, Buhrstone Group, 150 feet; 6th, Flatwoods and 

 Lagrange Lignitic Group, 450 feet, making a total thickness of 872 

 feet. The Lagrange and Porter's Creek Group of Safford is the same 

 as the Flatwoods and Lagrange Lignitic. The Buhrstone Group of 

 Tuomey is the same as the Siliceous Claiborne Group of Hilgard. 



The Eocence is followed by the Grand Gulf Group, probably- a de- 

 posit in brackish water, almost non-fossiliferous, and having a thickness 

 of 250 feet. 



Prof. Leo Lesquereuxf described, from the Green River Group of 



* Proe. Am. Ass., Ad. Sei. 



-;- 1872, U. S. Geo. Sur. of Montana, etc. 



