150 Treeless Areas of the Northwest— Leiherg. 



n great decrease in the annual rainfall and temperature, and a 

 gradual dying out of the forests. 



I have before noticed that the mean annual rainfall is proba- 

 bly yet sufficient to maintain a fair amount of forest growth, were 

 it only more evenly distributed. As it is now, much the greater 

 portion falls as snow or as very early or late rains, leaving nothing 

 for the growing season. Again the extremes of temperature in the 

 summer months is rather inimical to the successful growth of a 

 forest. The writer remembers well how a few years ago, in the 

 latter part of June, the thermometer registered in the shade 114 

 degrees for days in succession. The wind was blowing briskly 

 from the south, and was like a rush of hot air from an oven. All 

 kinds of native herbaceous plants dried up — cured on the stalk — 

 and the foliage of the trees partly wilted and fell off. A few days 

 later the mercury descended to the freezing point. 



Did this ancient Tertiary (?) forest extend east of the 

 Missouri river? This we do not know with certainty as the great- 

 er portion of the country here is so deeply covered with the drift 

 deposit, but from the occurance of beds of lignite in place, at var- 

 ious localities, it is reasonable to infer that it did, though perhaps 

 only in more or less scattered groves. Possibly the ridges now 

 called the coteavs are granitic in origin, and at this time presented 

 a bare rocky surface upon which a forest could not exist. 



The present timbered areas in the northwest are due in a 

 large measure to the vast quantity of water left behind by the 

 melting ice of the glacial period, in the form of numerous 

 marshes, ponds and lakes. The evaporation from these sources 

 tends to maintain a tolerably constant degree of atmospheric hu- 

 midity. This condition does not exist west of the Missouri. There 

 are no ponds or lakes to retain the moisture, which drains off as 

 rapidly as it falls. 



A question now suggests itself: Is this portion of the con- 

 tinent still rising, and if so what will the ultimate result be? 



We know that the earth's crust is constantly changing, eleva- 

 ting certain portions and depressing others. The Sierra Nevada 

 which may be considered the continuation of the Cascades, is said to 

 be rising at the rate of six feet in a century. There is nothing to 

 disprove the supposition that the ranges to the north and north- 

 east are not also rising in a more or less rapid ratio. 



The smoking volcanic peaks among the Cascades and the 



