52 ROUTE NEAR THE FORTY-SEVENTH AND FORTY NINTH PARALLELS. 



of the Rocky mountains, anil into summer rains at Fort Snelling. It is probable that the 

 Bitter Root range has a heavy winter precipitation, and, arresting a large proportion of the 

 moisture from the west, protects the Rocky mountains from it and from heavy winter snows a 

 circumstance favorable to the construction and working of a railroad through the Rocky 

 mountains in this latitude. It appears probable, too, that the greatest precipitation in this 

 region takes place during the latter part of winter and the early part of spring. Mr. Tinkham, 

 incrossing the Bitter Root range, found two and three feet of snow in the latter part of Novem 

 ber ; and, before he left the camp on the summit of the pass, (7,250 feet elevation) the snow 

 increased to the depth of six feet. 



The evidence adduced by Gov. Stevens shows that no obstruction to a railroad need be appre 

 hended from snow across the plains through the passes of the Rocky mountains, and thence by 

 way of the Columbia River Pass to Puget sound, though the great rise of the Bitter Root and 

 Flathead rivers and Clark s fork, in the spring freshets, indicates a large deposition of snow 

 at their sources. It is reported, that two winters previous to that of Gov. Stevens s party 

 beino- there, (winter of 1851-2.) a party of Flathead Indians were prevented from returning 

 to their village, in St. Mary s valley, although only two or three days travel from it, by the 

 passes being blocked up with snow ; they were on that account obliged to pass the winter in 

 one of the valleys east of St. Mary s. This does not, however, make it impracticable for a 

 railroad, since it was the accumulation of drift of the whole winter, and on a railroad track 

 it would be removed as fast as it fell. The meteorological observations made at Fort Benton 

 and in St. Mary s valley during the past year, will be interesting. The amount of winter 

 rains converted into snow, give pretty sure indications, in these climates, of the greatest depth 

 that may be encountered, allowing one foot of snow to one inch of rain. 



With respect to the temperature of the route : San Francisco, in about latitude 37, has a 

 winter temperature of 50 Fahrenheit ; Fort Moultrie, Charleston harbor, about latitude 33, 

 has about the same winter temperature, 50 Fahrenheit ; Steilacoom, Puget sound, about lati 

 tude 47, has a winter temperature of about 39 Fahrenheit the same, nearly, as that of 

 Fort Monroe, Old Point Comfort, Chesapeake bay, in latitude about 37, which is 40 Fahren 

 heit. 



The mean winter temperature of Steilacoom, Puget sound, is 39; of San Francisco, 50. 4; 

 showing an increase of aloout 1 of Fahrenheit for 1 of latitude, which is the change generally 

 on that coast within those limits, corresponding nearly with the eastern part of Europe, 

 as given by Humboldt. 



On the Atlantic coast, the change from south to north in our territory, as far north as Boston, 

 is about 2. 4 Fahrenheit for 1 of latitude. The meteorological observations that I have access 

 to, those of the Surgeon General s bureau, do not show whether this change of proportion takes 

 place gradually between the shores of the two oceans, or if it be sudden. 



Along the Mississippi river the decrease of temperature for increase of latitude is somewhat 

 less than on the Atlantic. 



Along the chain of the Rocky mountains the change of temperature in some instances corre 

 sponds with the Atlantic, sometimes with the Mississippi ; in other cases, the proportionate 

 decrease of temperature going north is greater than either. The observations on the northern 

 route, as given in the report, are too imperfect to enable a satisfactory comparison to be drawn 

 between them and those made at points further south. So far as any conclusions can be 

 deduced from them, they indicate that the law of change of temperature along the Rocky 

 mountain range for change of latitude is nearly the same as that along the Mississippi or the 

 Atlantic coast the points being reduced to a common elevation by the allowance of 1 Fah 

 renheit for every 300 feet of elevation. It is supposed, also, that no great modifying influ 

 ences from local causes exist such, for instance, as the Great Salt lake. If, then, we find 

 points along the northern route, among the mountains, with winter temperatures not exceed 

 ing those many degrees further south, in the same mountain chain, it will be due simply to 



