ORIGIN OF THE LOWLANDS OF THE YUKON. US 



including the numerous islands as well as the bordering country for many 

 miles, has been traversed by the river and is, in fact, a vast flood-plain 

 deposit. 



The sections referred to in the newly eroded banks show current-bedded 

 gravels and sands, with occasional interstratified layers of peat similar to 

 that now forming the surface layer beneath the forest. 



On looking down on the lowlands from hills near their border — the best 

 view that I obtained was from the summit of a hill about one hundred miles 

 up the Porcupine — one sees winding lanes opening out through the forest, 

 carpeted with bright green Equisetums, and overshadowed by tall spruce 

 trees or slim, gracefully bending willows. These picturesque lanes mark the 

 positions of recently abandoned water-courses. The most recent of these 

 old channels still hold ponds and sloughs, about which the moss grows with 

 great luxuriance. Those of older date are indicated by a change of tint or 

 a variation in the luxuriance of the forest trees, and may be easily recog- 

 nized in a wide-reaching view. 



The vegetation on the lowlands is composed mainly of spruce trees, grow- 

 ing close together and attaining a height of sixty or seventy feet or more. 

 Along the stream willows and alders are common, and wild roses bloom in 

 luxuriance in all. of the more open spaces. Beneath the trees and dense 

 undergrowth there is a thick, soft carpet of lichens and mosses, in which 

 thousands of lovely flowering plants unfold their blossoms and ripen their 

 brilliant fruits. Beneath the moss there is usually a layer of vegetable 

 mould or peat, ranging from a foot or two to many feet in thickness. Its 

 maximum depth is unknown. Beneath the immediate surface the peaty layer 

 is frozen throughout the year. It rests either on strata of loose material, 

 as sand or clay, or immediately on the subjacent solid rock. The dense 

 forest of spruce rising above the moss is about all that distinguishes the low 

 swamp lands along the Yukon from the tundra of the coast. There are dif- 

 ferences, however, in the luxuriant, cryptogamic floras of the two regions, 

 which are sufficiently obvious on close examination. 



The undermined and crumbling banks of the Yukon and tributary streams, 

 where they flow through the swampy lowlands, frequently exhibit sections of 

 ancient peaty layers, which are solidly frozen, and also the edges of strata of 

 clear ice. The trees growing on the undermined banks frequently lean far 

 over and dip their tops in the current before being finally carried away. At 

 times large blocks of the bank cave off and carry a number of trees bodily 

 into the river, where they sometimes remain standing half submerged for a 

 whole season. These slides are usually preceded by a crevassing of the bank 

 in lines parallel with its edge and distant some twenty or thirty feet from it. 

 The carpet of moss and rootlets that occurs throughout the lowlands, and, 

 we' might say without exaggeration, throughout Alaska, is so tenaceous and 



