APPENDIX D. — GEOLOGY. 167 



of black scorire and several other specimens of volcanic rocks. Drift 

 the same as on yesterday ; soil and subsoil arenaceous. 



June 16. — The surface was broken, and presented a number of sand- 

 hills. Saw to-day large quantities of drift, which did not differ in com- 

 position from that previously noticed. At about eight o'clock we came 

 to a long range of high bluffs, which, as we afterwards ascertained, 

 marked the borders of the "Llano estacado." They were composed of 

 horizontal layers of drift, sandstone, and yellow clay, (see Section No. 7,) 

 all of which seemed to be rapidly yielding to the weather. At the 

 base of the bluffs I observed a few small boulders composed of green- 

 stone porphyry. Soil and subsoil sandy. 



June 20. — During the first part of our route we travelled over a hilly 

 and broken region, consisting for the most part of a succession of sand- 

 hills, varying from ten to one hundred feet in height. At the distance 

 of five miles we reached a gradual ascent, which soon led us to the 

 summit of a high and slightly -rolling plain: over its surface were 

 scattered a great many fragments of white carbonate of lime, as well as 

 drift. From the latter I obtained specimens of agate, chalcedony, &c. 

 During the day I had frequent opportunities of observing the formation, 

 which uniformly consisted of drift, interstratified with horizontal layers 

 of red and yellow clay. Sometimes the drift exhibited a calcareous 

 coating, the same as before described. 



June 21. — Passed today a number of drift-hills, varying in height 

 from twenty to one hundred feet. The surface was very much divided 

 by ravines, with perpendicular sides, composed mostly of red clay, and 

 varying in depth from ten to fifty feet. Near our encampment I ob- 

 served a horizontal section of yellow loam, coarse conglomerate, and 

 red clay ; the last thickly reticulated with gypsum, and overlaid by a 

 terminating stratum of the same, (see Section No. 8.) Soil and subsoil 

 arenaceous. 



June 22. — Passed a large number of drift-hills. The country, as on 

 yesterday, was very rough, and much divided by ravines, some of which 

 were fifty feet deep. Their sides were generally composed of red clay, 

 overlaid by drift ; in a few instances they exposed seams of gypsum. 

 From the drift I obtained specimens of fossil-wood, agate, jasper, and a 

 few water-worn fossil shells of the genus Ostrea. Soil and subsoil the 

 same as before. 



June 23. — To-day we observed the gypsum frequently exposed. It 

 did not differ in character from that previously described, and was 

 always found overlying the red clay. Soil and subsoil arenaceous. 



