52 ROUTE NEAR THE FORTY-SEVENTH AND FORTY-NINTH PARALLELS. 
of the Rocky mountains, and 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, 
in crossing 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 Goy. 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 
being 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 about 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 
