94 EEPOET UNITED STATES GEOLOGICAL SURVEY. 



occupied, by the group decide me" to determiue it as sucli for the present. 

 If this should be proved by subsequent investigations not to be Per- 

 mian, it will necessarily be added to the lowest Mesozoic formation. 

 Although many miles were travelled during the past season in the "red 

 beds," we are not able to throw any additional light upon the question 

 touching their true position. The direct superposition of undoubted 

 Jurassic beds draws the limits rather closely, out we must still look for- 

 ward to some palseontological discovery that will set all doubts at rest. 

 In the preceding pages I have spoken of this formation or group as the 

 Trias (without query), but define this as not indicating that I desire to 

 commit myself upon the point. I am of the opinion that eventually this 

 identification may prove to be the correct one, but up to the present time 

 it is not yet established. 



The anticlinal axis, which has frequently been mentioned above, is a 

 very interesting feature of the region. As it passes beyond the limits 

 prescribed for this chapter, a connected discussion thereof shall be post- 

 poned until later. Jurassic beds are satisfactorily developed, occupying 

 a definite horizon between the red beds and the lowest group of the 

 Cretaceous formation. Although they do not compare favorably, from 

 a palseontological point of view, with the occurrences farther north, the 

 evidence obtained is entirely sufficient to establish its geological position 

 beyond a doubt. Groups younger than the Jurassic are developed in 

 regular succession and require no further mention. 



One of the most interesting features of the Wind Eiver Eange is found 

 in its evidence of abundant glaciation. No mountain region that I have 

 had occasion to visit in the West shows so strikingly the enormous effects 

 produced by the action of moving ice. Nearly the entire western slope, 

 so far as it lay within our district, must have been covered with suc- 

 cessive ice-fields. They have left their history written in unmistak- 

 able, ineffaceable language upon the rocks which once they covered. 

 Climatal conditions since that period have undergone a change, and 

 we are enabled by reading the writing transmitted to us to construct a 

 picture of what at one time must have been the conditions of this sec- 

 tion of the country. In the annual report for 1875 I have given my 

 views with regard to the former existence of glaciers in the Eocky 

 Mountains. Although based upon observations made in regions 4 and 

 5 degrees of latitude farther south, the general conclusions will apply 

 equally well here. 



Taken as a whole, the country to which this chapter is devoted is one 

 replete with interest. We miss in them, however, the occurrence of 

 erupted rocks. Whether the anticlinal axis has been caused by their 

 action, without their having broken through to the surface, may, for the 

 present, remain an open question. No evidence either for or against 

 such a supposition was obtained within the region above described. 



