advanced suggesting that the North basin was perhaps the last 

 to see glacial recession, hence the last to become vegetated. The 

 highly alpine condition of this basin is then perhaps due not to 

 climatic causes but to the recent disappearance of the local glacier 

 retained within its walls. It is only a question of time when the 

 record of glaciation in this basin will be deeply hidden by a 

 Picea-Abies mesophytic forest as it is in the South basin to-day. 



(e). The Picea-Abies Forest. The theory has been advanced 

 that the Krummholz is a mesaphytic combination and the evi- 

 dence has been drawn from the Picea-Abies forest of the region. 

 It may be well now to speak of this forest more in detail. In 

 our discussion of climatic factors we have noticed that this 

 combination, the resultant of a complex of factors, is the climax 

 mesophytic forest type of this region. The principal trees are 

 the black spruce, Picea nigra, and the fir-balsam, Abies balsamea, 

 which form the forest stand. Associated, but largely confined 

 to water courses, are Betula papyrifera cordifolia, and Alnus 

 z'iridis which form threads of light green woven into the darker 

 shade of the coniferous forest. The arbor-vitae, Thuya occi- 

 dentalis, occurs sparingly along water courses at the outer border 

 of the Great basin. It was recorded at an altitude of 2,800 feet. 



The forest floor is covered with a dense and contin- 

 uous mat of mosses consisting not of a multiplication of species 

 but chiefly of three forms. Hypnnm Schreberi, H. crista-castren- 

 sis, and Hylocomium splendens which recur continually in this 

 thick moss carpet, covering rocks and logs alike with an uninter- 

 rupted mat of green. In this carpet also occur several liver- 

 worts, Ptilidium ciliare and Bazzania trilobata being the most 

 prominent. On exposed rocks Dicranums are not uncommon. 

 Through this moss carpet, arising from the rich humus below, 

 extends a variety of forms. Pyrus americana, Amelanchier 

 oligocarpa, and nemopanthes fascicularis are prominent, the 

 abundance of seedlings of the former being especially noticeable. 

 Other less common shrubs are: Ribes prostratum, Viburnum 

 pauciftorum and Aralia nudicauHs. Taxus canadensis occurs 

 abundantly and in its characteristic habit of growth. Other 

 forms, which with the moss carpet constitute the forest floor, 

 are : Oxalis acetosella, Coptis trifolia, Maianthemum canadense, 



36 



