OF THE UPPER MISSOURI. 131 
one inch to seven feet. Over all this great district there are at the present time no large 
forests, no timber except that which skirts the streams. We now know that during the 
Tertiary period vast forests of timber must have covered many portions of the far West, 
from the abundance and variety of the vegetable remains preserved in the rocks. Silicified 
trunks of trees, fifty to one hundred feet in length and two to four feet in diameter, and 
stumps which indicate gigantic forest trees, occur abundantly over hundreds of square miles 
along the Missouri and Yellowstone rivers. Prof. Henry and other meteorologists have 
arrived at the conclusion, from a large number of well-authenticated facts, that the absence 
of forest trees on the great prairies of the far West is due to the want of moisture, which 
is well known to prevail all along the eastern slope of the Rocky mountains. The pre- 
vailing winds are now known to come from the west, and as the currents of air ladened 
with moisture from the Pacific ascend the western slope of the mountains, become con- 
densed and deposit their burdens for the most part before reaching the eastern slope. 
Prof. Henry, in his paper on Climatology, contributed to the Patent Office Report for 
1856, says: “The return westerly current, sweeping over the Pacific Ocean, and conse- 
quently charged with moisture, will impinge on the Coast Range of mountains of Oregon 
and California, and, in ascending its slopes, deposit moisture on the western declivity, 
giving fertility and a healthful climate to a narrow strip of country bordering on the ocean, 
and sterility to the eastern slope. All the moisture, however, will not be deposited in the 
passage over the first range, but a portion will be precipitated on the western side of the 
next, until it reaches the eastern elevated ridge of the Rocky mountain system, when, we 
think, it will be nearly if not quite exhausted.” We are now supposing that the climatic 
conditions—winds, currents of air, &c., did not differ to any great extent during the Ter- 
tiary epoch from those which prevail in the same latitudes at the present day. We there- 
fore venture the suggestion that up to the time of the accumulation of the middle Tertiary 
deposits the lofty barrier of the Rocky mountains did not exist. 
CHAPTER XIV. 
MINERALS AND GEOLOGICAL SPECIMENS. 
I. IGNEOUS AND METAMORPHIC ROCKS. 
1. Gneiss ferruginous, . C . 12m. N.W. Ft. Lar. ; 7. Felspar, flesh-colored from No. 6,. Rawhide butte. 
2. Micaslate, . 5 é q : do. do. 8. Granite, fine-grained, micaceous, . do. 
3. Mica, more micaceous, . : c do. do. 9. Granite, gray, . : 5 . Laramie hills. 
4, Granite, coarse, . : c . Laramie peak. 10. Quartz, white, . 0 : . do. 
5. Mica slate, with silvery mica, . 4m.N. Ft. Laramie. | 11. Hornblende slate, 9 : do. 
6. Granite, pulverulent, . 0 . Rawhide butte. 12. Hornblende rock, . ¢ : 0 do. 
