APPENDIX D. GEOLOGY. 163 



Immediately adjoining the creek the soil is good and very productive ; 

 but at a little distance from it, it is barren and sandy. 



May 26. — To-day we passed a number of sand-hills, varying in height 

 from ten to thirty feet. The only rocks met with were a few small 

 boulders, composed of quartz and greenstone. 



May 27. — The surface was in many places composed of detritus of 

 granite, quartz, and greenstone ; saw to-day a number of boulders, 

 mostly composed of hard granite, and presenting smooth and polished 

 surfaces. The largest was about fifteen feet in circumference, and would 

 weigh probably three or four thousand pounds. We frequently en- 

 countered local deposites of red scoriaceous rock. Captain McClellan 

 having visited one of the mountains, presented me with a specimen of 

 gray calcareous sandstone, which, as he informed me, he obtained from 

 a horizontal stratum of the same, situated within a few feet of the base 

 of the mountain. 



Thus far about twelve of the "Witchita mountains have been ex- 

 amined, and have been found to present a nearly uniform appearance 

 and structure. Composed of fine granite of various degrees of hardness 

 and color, they rise abruptly from a smooth and nearly level plain to 

 the height of eight or nine hundred feet. Many of them are isolated 

 and of an irregular conical shape, while others are grouped together in 

 small clusters, and are more or less rounded. At a distance they ap- 

 peared to be smooth, but upon a nearer approach their surfaces were 

 found to be quite rough, and presenting the appearance of loose rock 

 thrown confusedly together. In many places the granite was observed 

 occupying its original position, and was variously traversed by joints 

 and master-joints, which, intersecting each other at right-angles, gave 

 to the mass somewhat of a cuboidal structure. Soil rich, and from 

 three to four feet thick ; subsoil argillaceous and of a red color. 



May 28. — Did not move from camp. In the evening I explored a 

 short distance up and down Otter creek ; its bed is here composed of 

 horizontal layers of finely laminated sandstone, containing green and 

 yellow spots of the same character as those noticed on the 21st instant. 



May 29. — Passed a number of the mountains, several of which I 

 ascended and found composed of hard granite, variously traversed by 

 veins of greenstone porphyry and yellow quartz ; the last containing 

 small scales of mica. The sides of the mountains frequently presented 

 lofty precipices, one of which was divided from top to bottom by a vein 

 of greenstone nearly perpendiculaf, and about twenty inches thick. I 

 observed no change in the character of the adjoining prairie, except a 

 few local deposites of drift and detritus, from which I collected specimens 



