1 6 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



a position to give a detailed description of the botanical 

 characteristics of the different specimens, apart from noting 

 the distinguishing marks of the cones and of the i-year-old 

 seedlings. The description of the cones and the seedlings can 

 be conveniently prefaced by an account of the forest conditions 

 of the localities where the cones were collected. 



The relief features of British Columbia, some of which extend 

 the whole length of the province, and others only as far north 

 as the 54th parallel of latitude, have a north-west and south- 

 east trend and may, excluding the Peace River district in the 

 north-east, be described as consisting of five physiographical 

 units. 



The first physiographical feature is the Rocky Mountain 

 s.ystem extending northwards throughout the whole length of 

 the province. At the western base of the Rocky Mountains 

 is an enormous U-shaped valley, extending from the International 

 boundary in the south to the Yukon Territory in the north, the 

 floor of vi^hich has an average elevation of approximately 

 2400 feet above sea-level and an altitudinal range of 700 feet. 

 The valley is from 2 to 15 miles in width, and is flanked on 

 both sides by high mountains for the greater part of its length. 

 It is drained by several rivers with low passes between them. 

 In respect of size the valley is often out of proportion to the 

 streams that drain it. The direction of drainage is determined 

 by fault lines or zones which mark the boundaries between 

 different rock formations. 



This great trough, or intermontane valley, was brought to its 

 present form through long-continued erosion by valley glaciers, 

 powerful enough to ride over the divides between the former 

 heads of the streams, and to degrade them nearly to a common 

 level. 



The second physiographical feature is the Columbia system, 

 which lies to the west of the Rocky Mountains trench, but does 

 not extend farther north than the 54th parallel of latitude. This 

 system comprises the Cariboo Mountains in the north, and the 

 Selkirk and Monashee Mountains in the south. Separating the 

 Selkirk and Monashee Mountains is the well-defined Selkirk 

 trench or intermontane valley, which is occupied by the 

 Columbia River and the Arrow Lakes. The Selkirk Mountains 

 are dissected by several large structural valleys, the relative 

 physiographical importance of which has not been determined. 



