152 EEPOET UNITED STATES GEOLOGICAL SURVEY. 



CONCLUSION. 



Several features of great interest were observed in the Sweetwater 

 district. Prominent among these is that pertaining to the elevation of 

 mountain ranges and to great strati graphical disturbances generally. 

 IJepresented by the Wind Eiver Mountains we have a portion of the 

 main Eocky Mountain system. The structure of this range is essentially 

 simple. It is the direct jjroduct of an unequal anticlinal fold. Studying 

 the position where it is located, we observe some im])ortant facts. To 

 the north and northeast of the range the older sedimentary formations 

 rapidly assume very great vertical dimensions, while for a long distance 

 in the opi)osite direction they show a smaller development. Here, then, 

 we find an area of maximum sedimentation — one capable of i)roducing 

 the results which Sir John Herschel so ingeniously assumes, i.e., a down- 

 ward tiexure of the strata. This necessitates a corresponding upward 

 movement in order to re-establish equilibrium. Such a movement will 

 take place at the point or along the line of minimum resistance. In the 

 existence of the Prozoic subsidiary range we have an ancient barrier to 

 the influx of the earliest waters producing sedimentation ; consequently 

 we find along this old range a line least incumbered by deposition of 

 weighty sediment. This indicates the horizontal zone of least vertical 

 resistance, and here we find the Wind Eiver Eange occupjing a very 

 elevated position. From the structure of these mountains, as well as 

 from that of the sedimentary area east and northeast, we learn that thje 

 force which produced the upheaval made itself felt for a greater distance 

 eastward than west. This is shown by the long-continued easterly dip 

 of the strata and by the subsequent rearrangement of strata as produced 

 by the two easterly anticlinal uplifts. A result of this nature would 

 necessarily follow were the cause of the first distiu-bance located north 

 and northeast of the range. We observe in the range, as well as in the 

 anticlinal folds eastward, the lack of symmetrical arrangement of par- 

 ticipating beds. The axes of the folds, instead of standing vertical, in- 

 cline to the northeast, at augles from 20° to 30° from the vertical. Ex- 

 pressing the same fact in other words, we may say the movement 

 producing the elevation of ridges or ranges which show an anticlinal 

 structure has, in this instance, progressed from northeast to southwest, 

 and, we uiiij add, due to the intluence of endogenous flexure of deposits 

 caused by an enormous accumulation of sediment. 



As the two anticlinal folds which have been marked as A and B in pre- 

 vious pages approach the Sweetwater and Seminole Hills, the direction 

 of the vertical axis changes. It becomes first perpendicular, and then 

 inclines to the southwest. This, no doubt, is OAving to the existence pri- 

 marily of granites, which, in that region, have been elevated synchro- 

 nously or immediately before ; and, secondarily, to the masses of sedi- 

 ment which had an opportunity to accumulate to the southward. In 

 connection with the remaining two antichnals of our district (C and D), 

 we observe the same features that have been seen occurring near the 

 Wind Eiver Eange. The strata involved show a more rapid inclination 

 toward the west than the east. So far as the area which we examined 

 is concerned, we may regard it as a rule that the axes of anticlinal folds 

 trending north and south, with variations to the northwest, show a de- 

 cided dip to the east and northeast. It is a matter of some risk to base 

 generalizations upon observations exten<ling over even more than 10,000 

 miles. I am fully aware that investigations of contiguous regions may 

 prove the views held with regard to the elevation of the Wind Eiver 

 chain as untenable. The above demonstration, however, has suggested 



