METEOROLOGY OF THE FIELD EXPLORED. 131 



1S47- 4S ........................................................... below zero 28 



184S- 49 ......................................................... . , &quot; 37 



1849- 50 ........................................................... 31 



1S50- 51 ........................................................... &quot; 



At Pernbina, on the Red river of the North, and just under the 49th parallel, the winter climate 

 is somewhat colder than at St. Paul, the mercury freezing once or twice during each winter. 

 The spirit thermometer has shown a temperature of 52 below zero. The navigation of the 

 Red river closes from the 1st to the 15th November, and opens from the 10th to the 25th of 

 April. 



Westward to the Rocky mountains, the climate becomes milder and the quantity of snow is 

 less. In the immediate vicinity of Fort Union, the fall of snow is light; and the Missouri gener 

 ally freezes from the 20th of November to the 1st of December, and breaks up about the 1st of 

 April. Through the courtesy of the officers of that post, observations of the temperature, and of 

 the occurrence of ice and snow, will be kept for many months, which will hereafter give the 

 means of developing still further the meteorology of that region. 



At Fort Benton the climate is comparatively mild. But little snow falls, and the Fur Com 

 panies who have occupied that position for twenty years always carry their goods to their trading 

 posts in winter, on the Milk and Marias rivers, in wagons. They have a post on the Milk river 

 and at the forks of the Marias, the former about seventy-five miles from Fort Benton, a little 

 to the east of north, and the other about one hundred miles in a north-northwest direction. Even 

 on a, line much farther north, the quantity of snow is not excessive. Thomas Simpson, from 

 December 1, 1836, to February 1, 1837, made a journey of 1,277 miles, on a route between 

 latitudes 50 and - , from the Red river to Fort Chipewayan, on Lake Athabasca, 

 taking in his route Forts Pelby and Curlton. The weather was mild till December 16, and no 

 snow of consequence was on the ground till December 14. At Fort Pelby, near the source of 

 the Assiniboin river, the temperature on December 19th fell to 44 below zero. The route to 

 Carllon, which was reached on the 30th December, was over a rolling country, affording food at 

 times to countless herds of buffalo, the weather being intensely cold. Thence to Fort Chipe 

 wayan the route was through a wooded and most picturesque country, the weather at times mild 

 and rainy, the snows of the valleys soft, and the depth at Lake Athabasca about three feet. The 

 probable depth from Fort Carltori to this point was from two to three feet. 



I experienced great difficulty, both at Fort Union and Fort Benton, in getting information as to 

 the snows in the passes of the Rocky mountains, and as to the period when they were 

 practicable for horses. Even at Fort Union the employes of the expedition were disturbed by 

 assurances from the half-breeds in that vicinity, that they would find the snow knee-deep before 

 reaching Fort Benton, and that the Rocky mountains would be impassable. 



At Fort Benton most diligent inquiry was made of the members of the Fur Companies and of 

 the Blackfeet Indians. No person was found who had ever crossed the mountains later than 

 the first days of November, or earlier than the first days of April. The general opinion was that 

 the snows were some twenty feet deep from November till April, and sometimes till May. But 

 as no person could speak from positive observation, it became necessary to determine the 

 question experimentally. 



Winter posts were therefore established at Fort Benton and in the St. Mary s valley, under 

 the direction of Mr. James Doty and Lieutenant Mullan, and, in accordance with his own 

 original suggestion, Lieutenant Grover was directed to leave Fort Benton in January, and cross 

 the ranges to the Pacific with a dog train. 



On reaching the St. Mary s valley, information was received from the Flathead Indians that 

 the passes were generally practicable with horses throughout the winter. There has been no 

 communication whatever between Fort Benton and the St. Mary s valley. The Flatheads never 



