8T.J0HN.] . LINCOLF AND BLACKFOOT DIVIDE— SECTION. 331 



]S"ear our southern border tliis belt rises into rather prominent ridges 

 which culminate to the south, where they seem to bridge over into 

 Mount Putnam in the water-shed between the Eoss Fork and Portneuf 

 drainages. Just to the north, however, the upland exhibits a broad 

 swell over Avhich the Fort Hall and Soda Springs road passes from the 

 head of Lincoln Valley, and which was found to be capped by Jurassic 

 deposits, which occupy a shallow synchnal flanked on the east by Up- 

 per Carboniferous strata more steeply inclined westward. 



The strike of the strata in this part of the ridge is very variable, yet 

 with some persistency even in its variableness. As we pass obliquely 

 across the divide from a point near our southern line northwesterly to 

 the head of Lincoln Yalley, the strike in the Carboniferous border de- 

 posits swerves round from N. 30° E. to HJsT. 20° W. as we reach the axis 

 of the Jurassic ledges, beyond which, in the slope descending to Lincoln 

 Yalley, the beds again strike about northeast and southwest, dippiug at 

 a moderate angle to the southeastward. It is, therefore, evident that 

 this portion of the divide owes intimate connection with the Putnam 

 ridge. But passing only a few miles farther north, in the monoclinal 

 ridge flanking the northeast side of Lincoln Valley there were observed 

 evidences of an abrupt change in the direction of the disturbing forces 

 accompanied by extraordinary local disturbance, resulting in the strata 

 being upraised and folded along a line bearing north of west and south 

 of east, mth local variations in the strike and degree of inclinal which 

 it would require much time thoroughly to decipher. 



In the southwest slope of this ridge, even within comparatively short 

 distances, of but a few score of yards in some instances, the strata are 

 warijed from a northerly to north-northeast inclination of 25'^ to 50° to 

 a dip in the opposite direction at angles varying from 65° to 80°. It is 

 possible, as has been suggested by Professor BracUey, whose examinations 

 in this quarter were much more extended than my own, that the steei^ 

 southerly dips here noticed mark the position of the dragged and up- 

 turned edges of the strata along a line of faulting the downthrow of 

 which was to the south, though to what vertical extent was not ascer- 

 tained. For the clearer illustration of the facts referred to, the accom- 

 panying sheet of diagrams is introduced, which represents the rock 

 sections observed in the north-side ridge on Lincoln Valley or Four- 

 Mile Creek, from Station III to a point a mile or two to the northwest, 

 two or three miles beyond which the Jurassic spur terminates in the 

 sage-plain bench east of the Lincoln. At the latter point the limestone 

 strata show variable dips, at one place the beds pitching steeply east- 

 ward at an angle of 50°, while in a short distance south they incline 

 more gently southward. In the southwest slope of Station lU, the fol- 

 lowing section of Jurassic strata occurs : 



Section at Station III. 



1. Long grassy slope to Four-Mile Creek, no rock exposiu-es. 



2. Gray, heavy -bedded limestone, in two layers, exposed 4 feet; dip 

 K. 25° Eo., at an angle of 20° to 25==". This ledge appears at a level of 

 about GOO feet below summit of station, and containes a large Pseudo- 

 monotis or Aviculopecten^ a small Gryjyhaa or Ostrea, Cam^rtoncctes, and 

 Lingula. 



3. Layers of brown, weathered, gray limestone, interbedded with 

 clayey matter, obscurely exx)osed in sloi^e. The limestones also contain 

 Fseudomonotis. 



