CHAPTER XIV. 



Meteorology of the Field Explored. 



The meteorology of the field covered by the exploration is one of the most interesting, as it 

 is one of the most important subjects of inquiry. It is not obstructed by deep snow, nor is 

 the temperature as low as has been generally imagined. There is a great depression in the 

 whole mountain chain of the Rocky mountains, the higher plateaus being nearly three thousand, 

 and the lower two thousand feet above the sea; whereas, at the 41st parallel, the higher 

 plateaus are six thousand, and the lower and more general ones are four thousand five hundred 

 feet above the sea. The greatest elevation of the Rocky mountains is south of the South Pass, 

 in latitude 39 to 40, where the Platte, the Rio Grande, the Arkansas, and the Colorado of the 

 Gulf of California have their rise. The mountain chain then rapidly declines to near the 48th 

 parallel. The temperature of the Rocky mountains at this parallel is as mild as any part 

 down to the 35th parallel of latitude. Moreover, on the western coast, the prevailing westerly 

 winds and the currents of the Pacific ocean, similar to, though less known than the Gulf 

 Stream, have modified the climate to such a degree that the isothermal lines run nearly parallel 

 to the coast, making the climate of Puget sound nearly if not quite as mild as that of San 

 Francisco, and causing it to correspond with that of the western coast of Europe in the same 

 latitude. Puget sound and Vancouver s island are strikingly like Ireland and West Shetland in 

 temperature; the first locality having a, mean temperature for July of 65, while Dublin has but 

 60, and the British islands range from 57 to 63. At Sitka, in Russian America, the mean of 

 winter at 35, and the summer mean of 56, correspond to the north of Ireland and Scotland. 

 The effect of this amelioration of temperature not only extends to the Rocky mountains, but is 

 felt on the eastern slope and for some distance .on the plains, where, in turn, it is met by the 

 temperatures from the Atlantic sweeping over the vast interior continental areas, growing some 

 what colder till the western end of Lake Superior and the Red river settlement of the north is 

 reached, and then growing milder till it meets the temperatures from the Pacific at an equilibrium. 



As regards the distribution of rain and snow, much of the moisture is deposited before reaching 

 this high latitude, except on the coast, where there is a large local precipitation ; and the Cas 

 cades mountains of Oregon and Washington arrest much of the rain that would be distributed 

 farther in the interior, especially in winter; and, as a consequence, the Rocky mountains in that 

 latitude have little winter precipitation, and the plains eastward have still less. The general 

 plateau from the head of the Mississippi westward, to and including the Rocky mountains, has 

 indeed the least winter precipitation of any portion of the continent, and can furnish no accu 

 mulation of snow from the two or three inches of water falling in a frozen state in the winter 

 months. 



The latitude is too high up for a large amount of precipitation, except near the coast. The 

 great summer precipitation of the upper portion of the Mississippi valley shows the line of pro 

 fuse rains to be at its farthest point northward there at that season of the year. On the plains 

 it extends farther north into British America, and on the coast of the Pacific it stretches from 

 Sitka northward nearly over the whole line of the coast. 



From these general facts of distribution of the water falling in rain and snow in the extreme 

 seasons, the observed facts of the winter climate of the interior are seen to have merely their 

 natural place. Little accumulation of snows can exist in the interior of these latitudes, at what- 



