34 
GEOLOGY. 
returned towards the mouth of Ocoya creek, and arrived in the evening, having had a hard 
ride of about fifty miles. In numerous places over the plain there are dry water courses or 
canals in the clay, and groves of dead cotton-wood trees. It is probable that the whole region 
has been subject to overflow. It should he observed that the water of the slough, or lake, was 
more or less saline, incrustations being found around the roots of the tufts of grass, where evapo¬ 
ration had proceeded rapidly. Specimens of scoriaceous cinder, or volcanic slag, were also 
found lying on the clay surface of the plain. 
August 14, Sunday .—The thermometer indicated a temperature of 102° in the shade during 
the middle of the day ; and a hot dry wind was constantly blowing from the west, following the 
course of the valley of the creek. 
August 15.—Examined the strata up the creek and on the right hank. The hills are in all 
respects similar to those on the left. At one point, however, an outcrop of coarse-grained sand¬ 
stone and conglomerate was found ; it was harder than the other strata, and modifies the 
outline of the hills. At sunset clouds were seen over the mountains at the east. The day was 
unusually warm, the thermometer standing at 104°. 
August 16.—Collected more fossils, and made drawings of them ; they are evidently Tertiary, 
and probably quite recent—Miocene or Pliocene. Fresh water shells are abundant in the pools 
of the creek, and specimens were preserved. 
August 17 and 18.—Obtained the order of succession and lithological characters of the strata 
forming one of the highest hills on the left hank of the creek. The edges are fully exposed in 
several places, and in others are partly obscured by soil. 1 Just before sunset we had a short 
shower, and the clouds looked very heavy over the mountains. 
August 19.—Made more extended excavations in the bed of fossils, and procured five or six 
additional species. Most of the specimens became broken and mutilated in taking them out. 
Some very large pectens were found, six inches in diameter ; one of these was drawn by Mr. 
Koppel. While he was turning over one of the masses of sandstone he was stung by a scorpion, 
carrying a great number of little ones on her hack. The application of a little ammonia water 
quickly relieved the pain, and no further inconvenience was experienced. 
August 20.—Found an additional number of species, and among them a shark’s tooth. 
Specimens of transparent selenite were obtained from the tops of some of the hills and from 
the bed of the creek. The water in the deep holes has now become very low, and is strongly 
impregnated with sulphur. It has the odor of sulphuretted hydrogen. Thermometer 103° in 
the shade. A comet was visible in the west this evening. 
August 21.—The night was cold, and at sunrise the thermometer stood at 56 degrees. The 
wind was blowing from the northeast, or down from the mountains, and this is generally the 
case early in the morning. 
August 27.—I have been prevented by illness from making any geological observations for 
several days. The sudden and great transitions from a temperature of 103° and 104° during 
the day to 40° and 50° at night, together with the use of stagnant water, are sufficient to pro¬ 
duce disease. On the evening of the 25th, I set up a pan of water in the shade of the brush- 
shed, in order to determine, if possible, the rate of the evaporation of water during the day. 
The hunters came in from the plains, bringing six fine carcases of deer and antelope, one of 
them a fat buck, weighing, when skinned, 115 pounds, and his hind-quarters over 60. It was 
of the black-tailed species. 
1 This section is described in Chapter XIII. 
