APPENDIX D. GEOLOGY. 171 



broken exterior, they were more or less rounded, and exhibited a gradual 

 slope to the prairie-level, while the granitic structure almost entirely 

 disappeared, its place being occupied by that of fine porphyry of a 

 reddish color. Scattered over the prairie were observed a great many 

 fragments of granite, greenstone porphyry, and quartz. The beds of 

 the different creeks were in many places covered with black ferruginous 

 sand, as well as large fragments of quartz, porphyry, and hornblende. 

 Soil black and very fertile; subsoil argillaceous. 



July 18. — The mountains presented the same appearance and struc- 

 ture as on yesterday. At about 8 o'clock we arrived at Cache creek ; 

 its bed was thickly strewn with black ferruginous sand and large frag- 

 ments of igneous rock. From the water's edge rose abruptly a long 

 line of smooth perpendicular cliffs, varying in height from three to four 

 hundred feet, and having in some places a slight columnar structure, 

 (see Section No. 11.) Upon examination they were found to be com- 

 posed mostly of fine porphyry of a reddish color, which was traversed 

 by parallel and nearly perpendicular veins of cellular quartz, varying in 

 thickness from two to three feet. Upon its exterior the quartz presented 

 a deep iron-rust color ; but when recently fractured, it exhibited various 

 shades of gray and brown, together with small shining particles of 

 sulphuret of iron. Soil fertile, and in some places three feet thick ; 

 subsoil argillaceous. 



July 19. — I spent the greater part of the day in exploring Cache 

 creek. About one mile below our present encampment I came to the 

 termination of the cliffs. A short distance below this I observed a 

 nearly horizontal stratum of coarsely laminated sandstone, fifty feet 

 thick, and including in its composition fragments of igneous rock of the 

 same character as that composing the cliffs ; the intermediate space 

 being occupied by red clay, which, as before, appeared to underlie the 

 sandstone, (see Section No. 11.) 



July 20. — Two miles below our camp of last evening I observed a 

 section composed of horizontal layers of gray sandstone, containing in 

 its composition small fragments of igneous rock. Six miles from this we 

 struck a seam of gypsum, varying in thickness from six to twelve inches. 

 Soil fertile ; subsoil composed of red and yellow clay. 



July 21. — During the day we met with frequent exposures of the 

 sandstone and gypsum. They presented, however, nothing different 

 from what has already been described. Soil and subsoil the same as 

 on yesterday. 



July 22. — Formation the same as on yesterday. 



July 23. — Did not move from camp. 



