APPENDIX D. GEOLOGY. 165 



June 3. — To day we came to a range of high bluffs about six miles 

 in length, and extending in a direction nearly parallel with the river. 

 At a distance they resembled a long line of fortification ; upon examina- 

 tion they were found to be composed of horizontal layers of red and blue 

 clay, thickly inters tratified with snow-white gypsum, (see Section No. 5.) 

 These bluffs appeared to be rapidly yielding to the weather : along 

 their base were thickly strewn large cuboidal masses of gypsum — some 

 ten feet in diameter — that appeared to have been but recently detached 

 from a stratum of the same near their summits. In the blue clay I 

 observed a thin seam of carbonate of copper. The gypsum was also 

 in a few places slightly tinged with the same metal. In a southerly 

 direction, and at the distance of about fifteen miles, we observed another 

 range of gypsum bluffs : they appeared to run in a direction parallel 

 with those already described. The intervening country was very rough 

 and broken. Soil dark and fertile ; subsoil argillaceous. 



June 4. — Passed a number of bluffs of the same composition as those 

 observed yesterday. The surface during the greater portion of the 

 march was whitened by gypsum, which was always found occupying its 

 position above the red clay. In the evening I visited a small hill, situ- 

 ated about three miles from camp, and succeeded in discovering a thin 

 seam of copper ore, as well as large beds of selenite. Soil and subsoil 

 the same as on yesterday. 



June 5. — The country travelled over to day was mostly composed of 

 sand-hills, varying in height from ten to sixty feet. On the middle 

 branch of Red river we saw long ranges of bluffs, which, upon examina- 

 tion, proved to be of the same character and composition as those seen 

 on the 3d instant. Soil and subsoil arenaceous. 



June 6. — To-day we passed a number of bluffs composed of red clay; 

 I did not observe any gypsum in their composition. As we progressed 

 the country gradually became more elevated. Here, for the first time 

 since leaving the Witchita mountains, we met with large quantities of 

 drift, composed principally of quartz and mica-schist. On Red river we 

 saw a fine section, fully exposed, showing a horizontal sub -stratum of 

 coarse-grained sandstone, overlaid by drift; the latter forty feet thick. 



June 7. — Formation the same as on yesterday. 



June 8. — Passed a number of ravines, the sides of most of which 

 were composed of red clay. At about 8 o'clock we came to a small 

 eminence in the prairie, near which I observed an outcrop of grayish- 

 yellow sandstone, presenting a dip of forty degrees to the west. The 

 surface was thickly covered with drift. I saw a number of boulders 

 composed of coarse and fine conglomerate, the largest of which meas- 



