NOTES ON THE DOUGLAS FIR. 1 7 



Of those, the Purcell trench is the most important from a 

 forestry point of view. 



The third physiographical feature lies between the Monashee, 

 Cariboo and Rocky Mountains on the east, and the Coast 

 Mountains on the west. This area is divided into three parts 

 from south to north, the Interior system to the 54th parallel of 

 latitude, the Cassiar system to the 59th parallel, and the Yukon 

 system north of this. The first of these only will be referred to 

 here. 



The Interior system or Plateau is approximately 500 miles in 

 length, varies from 140 to 170 miles in width, and is flanked by 

 the Cariboo and Monashee Mountains on the east, and the 

 Cascade Mountains on the west, merging gradually into the 

 mountains on either flank. 



The fourth physiographical unit is the Coast Mountains, which 

 border on the Pacific Ocean from the Fraser River to the head 

 of the Lynn Canal in Alaska. Another great intermontane 

 valley separates the Coast Mountains on the mainland of British 

 Columbia from the ranges occurring on Vancouver Islands,. 

 known collectively as the Insular system. This valley, although 

 submerged off the British Columbia coast, appears as a land 

 trench further southwards, after passing through Puget Sounds 

 and separates the Olympic Mountains from the Cascade 

 Mountains in Washington. The numerous fiords on the coast 

 of British Columbia are drowned or submerged river valleys, 

 similar to the great lochs on the West Coast of Scotland. 



The fifth physiographical feature is the Insular system. 



The influence of the physiographical features is of paramount 

 importance in connection with the distribution of the forests and 

 of lumbering. The mountains have a general trend alternating 

 with plateaux or mountain trenches all at right angles to the 

 warm moisture-laden winds. This arrangement of the chief 

 physiographical features is of the greatest significance in 

 exercising a controlling influence on the factors of climate, 

 temperature and moisture, and so determining the distribution 

 of the different types of forest. The broad U-shaped valleys 

 throughout the province are of vital importance from the stand- 

 point of lumbering. They determine the locality of depots for 

 the accommodation of raw forest products for manufacturing 

 purposes, while the valleys themselves or their slopes, and the 

 lower ends of the valleys debouching into them, furnish the 



VOL. XXXVI. PART 1. B 



