209 



shown iu the extensive acreage of fallen timber. On the other hand, I 

 know of no region throughout the liocky Mountains where the condi- 

 tions seem so favorable for a young growth. During the five years that 

 1 liave carefully observed the forests nothing has so impressed me as 

 the rapid, healthy development of the young trees which in a few years 

 replace the down timber. In most instances the young growth be- 

 longs to Pimis Murrayana, and in every case it is the first tree to spring- 

 up over a burnt district, 



I need not enter here into a lengthy discussion of the influence of 

 the forest upon the supply of water. I simply desire to call your at- 

 tention to the special advantages of the Yellowstone Park forest for 

 maintaining a water supply of a country singularly well situated to 

 gather and distribute a large annual precipitation of moisture. This 

 uplifted mountain mass measures 90 miles in length by 60 in breadth. 

 From the southwest the moisture-laden winds blowing across the Mad- 

 ison plateau precipitate immense quantities of snow and rain over the 

 cold, wet tableland. Storms gather over the mountains at all times of 

 the year. The annual precipitation is excessive as compared with the 

 adjacent regions of the Eocky Mountains. Eains are of common oc- 

 currence between May and September, while during eight mouths of 

 the year nearly all precipitation falls as snow, which lies upon the 

 ground well into midsummer, and on the northern slopes, at higher 

 altitudes, remains throughout the year. Frosts occur nearly every 

 week during the summer, and observations in July and August for sev- 

 eral seasons, at various stations over the plateau, show that the mini- 

 mum thermometer registers below 40^^ every night. 



The forests exert a powerful influence in sheltering the snow fields, 

 marshes, and meadows from the direct rays of the sun and the dry 

 moisture-absorbing winds blowing from the west. Strip the plateau and 

 mountains of timber, and early freshets would soon lay waste the lower 

 country in spring and leave it arid and parched throughout the summer 

 and autumn, i^ot only would streams diminish, but the loose gravelly 

 soil which now everywhere covers the Park would rapidly be washed 

 away, laying bare the underlying rocks. The soil, with the accompanying 

 roots and grasses, playing the part of a sponge, exert a powerful influence 

 in maintaining the water supply. They serve to keep the ground cool 

 and moist and allow the water to percolate slowly from the surface to in- 

 numerable springs below and thence to the reservoirs of the great rivers. 



With a view of determining with some degree of accuracy the volume 

 of water flowing from the Park, the largest lakes and streams were care- 

 fully gauged. The measurements were made in early September, 1886, 

 not only the dryest period of the summer but the dryest season known 

 at any time within the previous five years. Evidence was ample to 

 show that Yellowstone Lake had fallen 20 inches below high-watermark 

 of early July, Measurements were made of the discharge from the lake 

 at a point on the river about one-quarter of a mile below the outlet. 

 24738— -Bull 2—14 



