316 METEOROLOGY. 
and the difference of latitude and elevation would show that the winter of 1833— 34 was some- 
what below the average for Fort Clark, even supposing it to be influenced less than Fort,Union 
by the western climatic characteristics which probably reach it to some extent. 
The late surveys of Lieutenant Warren in Nebraska demonstrate that a large portion of the 
country put down as arid plains in Mr. Blodgett’s charts is really occupied by the Black Hills, 
a tract of mountainous country well wooded with pine forests on its higher parts, and many 
portions of it tillable. " 
The influence of this correction can be scarcely estimated without further exploration of the 
country west of it, but it may be supposed to be very considerable. The greater cold of the 
winters at Forts Clark and Pierre may be accounted for by the fact that the hills favoring the 
precipitation of more snow and intercepting the mild westerly winds, which, having here a 
much wider and higher tract of mountaius to cross than they have either to the north or the 
south, naturally permit a more free scope to the cold winds from the northeast. 
If the isochimenal lines of 20° and 25° are to be connected at all between the Mississippi 
and the Upper Missouri, they must run west of these Black Hills across a low tract of country 
supposed to exist there, but which is yet quite unexplored. 
The chart for winter in the Surgeon General’s Meteorological Register appears to express 
much more nearly the direction of these lines, as determined by the latest observations, than 
those given by Mr. Blodgett himself. 
The temperature, both of Fort Kearney and Fort Riley, appear too high for winter, and the 
observations of three additional years lower them both considerably. Forts Benton and Laramie 
. hold a similar position in relation to each other, and seem to be wholly influenced by the climate 
of the western part of the continent. The following table shows their correspondence, and is 
not altered from the data used by the Surgeon General and Mr. Blodgett. "The intervention of 
a wide tract of unexplored mountainous country makes it impossible to connect the lines, with 
any approach to certainty, between these posts and those towards the east. 
iu E 
= 2 . " 
Means for 1853754. 3 2 E 5 5 E " а Remarks. 
= Б в Ж Е a = * : 
‘STR ТЕ 1.3 IR 
a, < Е н 
v e | e n Feet. . o m ж "s 
At Fort Вепоп......................... 47 49 | 110 36 | 2,780 49.9 | 72.8 | 44.5 | 95.4 | 48,9 | One year’s observations. 
At Fort Laramie.. sie 12 | 104 47 | 4,519 | 49.1 13.1 50.8 30.2 50.8 | Six years’ observations; mean, 50°.1. 
tes. 22% iE Oram 
The winter of 1853-54, at Fort Laramie, was below the mean, and the same may be assumed 
of that at Fort Benton—an assumption which is supported by the results of the observations 
during the following winter at Fort Owen, alluded to hereafter. Thus the mean winter temper- 
ature at Fort Laramie, for six years, was 310.1. 
The next points westward which admit of comparison are Fort Owen and Cantonment Ste- 
vens, both in Bitter Root valley, and only fourteen miles apart, with Fort Hall, on Snake river, 
and Salt Lake City. It must be remarked that the only winter observed at Fort Hall (1849—50) 
seems to have been unusually cold at Fort Laramie, the nearest point recorded, and two degrees 
may be allowed as the true correction for the mean winters at that place. This is not, however, 
made in this table. | | 
