METEOROLOGY OF THE FIELD EXPLORED. 131 
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At Pembina, 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 lst 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 Ist 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 Carlton. 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 
Carlton, 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 Carlton to this poimt 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 employés of the expedition were disturbed by 
assurances from the half-breed: 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 
