24 



METEOROLOGY. 



Pierre series, and the difference of latitude and elevation would show that the winter of 

 1833-34 was somewhat 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 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, both by the fact that the bills favoring 

 the precipitation of more snow and intercepting the mild westerly winds, which, having here 

 a much wider and higher tract of mountains 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 by 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. 



The winttjr 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 31° 14'. 



The next points westward which admit of comparison are Fort Owen and Cantonment Stevens, 

 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. 



