Page:The Journal of geology (IA journalofgeology11893univ).pdf/239

is known to be about an hundred inches. In the vicinity of Mt. St. Elias it is probably even greater than this. The prevailing winds are from the south, at least in summer, and are laden with moisture which is precipitated when the mountains are reached. To the north of the mountains the climate is far different from what it is on the coast. The summers are short and hot and the winters marked by extreme severity; the rain-fall is small throughout the year and perennial snow is not seen even on mountains four or five thousand feet high and situated near and even north of the Arctic Circle.

On the mountains facing the ocean the winter snow extends down to sea level but melts during spring and summer so as to form a well defined boundary, or "snow line," which recedes from the coast as the warm season advances. In August and September it has an elevation of about 2,500 feet, corresponding on the glaciers with the lower limit of the névés. The regions below and above the snow line are in marked contrast. From the ocean up to an elevation of from 2,500 to 3,000 feet in summer, every island in the ice as well as the low lands along the coast and even the moraines on the lower border of the Piedmont ice-sheet, are covered with luxuriant vegetation, and are frequently brilliant with banks of flowers. Above the snow line except on occasional sunny slopes at comparatively low elevation, where Alpine flowers thrive, all is desolate, lifeless winter. The well known features characteristic of glacial ice and névé snow are sharply defined by the same horizon. In the higher mountains snow storms are frequent even in summer, and at elevations exceeding about 13,000 feet rain never falls and the snow is fine and dry. On the mountain tops the snow does not soften, even on hot summer days. Its indefinite accumulation is prevented by avalanches and by its being blown away.

The relief of the St. Elias region is due largely to displacements. The mountains are in many instances formed of tilted blocks bounded by faults, and the prevailing structure approaches the Great Basin type. The effects of pre-glacial stream erosion are not distinguishable and in many instances the ice drainage is