64 THE ROYAL SOCIETY OF CANADA 



occupy them, which is contrary to the results of normal stream 

 erosion. 



The general trend of the regional drainage is toward the trench, 

 except in the case of the Kootenay River and the Columbia River, 

 which break through the western wall of the trench, and reach the 

 Pacific, while the Peace River cuts through the eastern wall, and finally 

 reaches the Arctic Ocean. The latter stream is the only one which 

 drains eastwards across the Rocky Mountains, suggesting that it is 

 antecedent in origin. This fact throws a flood of light on the origin of 

 the transverse valleys of the Rocky Mountains. 



The width of the trench averages 4-6 miles, but in places such as 

 the St. Mary's prairie near Cranbrook, in southern British Columbia, 

 and in the stretch from Tête Jaune Cache to Fort George, it is much 

 greater. The floor of the trench is usually flat or slightly rolling, and 

 is covered generally by the unconsolidated gravels and silts of the 

 Cenozoic. The walls of the trench usually rise abruptly from the floor, 

 especially on the eastern side, where it is usually precipitous. This 

 feature is most noticeable in the southern part of the trench. 



Early Exploration of the Rocky Mountain Trench 



The first European to discover the Rocky Mountain trench was 

 Sir Alexander Mackenzie, who entered it in the year 1793 by way of the 

 Peace River, travelled southward to the Fraser, which he followed for a 

 short distance, whence he turned westwards and reached the Pacific 

 coast. Thus Mackenzie was the first man to cross the great Cordillera 

 north of Mexico. This route into the mountains was followed for 

 many years by other explorers, including Fraser in 1806-07, Harmon 

 in 1820, Sir George Simpson in 1828, Capt. W. Butler in 1872, Horetsky 

 and Macoun in 1874. The southern portion of the trench was explored 

 by David Thompson in 1807, Alexander Henry 1811-1814, and Sir 

 George Simpson in 1841. The latter entered it near the Columbia 

 Lakes, the source of the Columbia River, and followed the depression 

 southward along the Kootenay River beyond the 49th parallel. 

 Palliser, who explored the Rocky Mountains during the years 1857-59, 

 was the first observer to remark the peculiar unbroken continuity of 

 this great structural feature. He recorded his observations in the 

 following words : 



"This great valley, through which the Columbia River flows, is 

 one of the most singular features observed on the west slope of the 

 Rocky Mountains. It is continued to the south from Columbia lakes, 

 by the valley through which the Kootenay River flows, and the famous 

 wintering grounds in the Bitter Root valley, to which the settlers 



