358 EEPOET UNITED STATES GEOLOGICAL SURVEY. 



fine detrital material and soil which supports a fair growth of herbage, 

 while in the hills a few dwarfed pines and groves of aspen are found. 



The ridge defining the southwest side of the Little Blackfoot Valley 

 originates in the low basaltic divide at the head of Willow Creek, and 

 which separates it from the southern terminus of the Blackfoot Range, a 

 few miles to the northwestward. This ridge has a course nearly parallel 

 with Gray's Lake ridge, northwest and southeast, in which latter direction 

 it is projected into the bend of the Blackfoot, a few miles south of the 

 south line of the district. Like the previously described ridge, it is 

 broken down near the middle, where it is crossed by a somewhat higher 

 pass, with steeper approaches, just over our southern border, to the 

 northwest of which it culminates in an irregular crest 7,000 to 7,000 feet 

 altitude above the sea, or 600 to 1,200 feet above the plain. A section 

 carried across the ridge at a point between the pass and one of the cul- 

 minating summits a mile to the north, on which Station XXIX was 

 located, is given below : 



/Section across Station XXIX ridge. 



1. Dark bluish gray, spar-seamed limestone, with concentric siliceous 

 nodules, passing upward into a very hard fragmentary siliceous rock. 

 Occurs as a heavy ledge flagging the south-facing slope descending into 

 the gap, and dips 35°, S. 25° E. The rock is complicated by joint struc- 

 ture and cleavage, the principal planes of which incline at an angle of 

 70°, X. 70° E. 



2. Slope, unexposed. 



3. Limestone, obscure exposure. 



4. Heavy bed of buff siliceous rock. 



5. Light bluish-gray spar-seamed limestone, forming a heavy bed the 

 outcrop of which is traced in a line of low cliffs which rise into Station 

 XXIX. A thickness of 50 feet is exposed in the mural face of the out- 

 crop, in which atmospheric erosion has scooped miniature caverns and 

 niches. Dip 45° to 50°, S. 65° W. The rock affords numbers of a large 

 species of Zaphrentis, which was the only fossil a hurried search detected. 



6. Space 200 yards across, showing gray cherty limestone and reddish- 

 buff siliceous deposits. Dip 30° south westward. 



7. Bluish-gray, spar-seamed, cherty limestone, a heavy ledge, exposed 

 20 to 40 feet, and dipping 30°, S. 50° W. Contains a minute Uetzia, 

 Hemipronites, and crinoidal columns. 



8. Slope, about 100 yards across ; no rock exposures. 



9. Limestone, similar to bed Xo. 7, appearing in crest of ridge about 

 southwest of Station XXIX, over a space perhaps 300 yards across. 

 Dip 50° to 65°, S. 50° W. Contains a small Zaphrentoid coral. 



10. Grayish-blue limestone and buff siliceous deposits, forming a heavy 

 deposit 300 to 400 yards across in the south flank of the ridge. Dip 

 55°, S. 45° W. 



11. Intensely hard, brittle, hornstone-like rock, much fractured trans- 

 versely, its outcrop presenting a dike-like appearance, exposed thick- 

 ness 5 feet, and clipping S. 35° W. at an angle of 65°. This rock is pre- 

 cisely like a ledge observed in the southwest foot of Blackfoot Peak, 

 with which it is believed to be identical. 



12. Limestone, obscurely exposed in foot of steep slope, where it merges 

 into the basaltic bench, over which the declivity descends thence into 

 the upper basin of the Blackfoot in a series of more or less distinct low 

 terraces. 



The above section crosses the ridge nearly at right angles to its trend, 



