GEOLOGY. 303 



of part of their moisture, but they meet with the rarefied air of the cen- 

 tral plains, and consequently rise higher and evaporate into thinner vapor. 

 There are few spots, however, which are wholly destitute of vegetation, 

 and large trees are frequent. There is no district which does not main- 

 tain its flocks of wild animals; but the diminution of even one or two 

 inches of rain in the year is most severely felt. The author came to the 

 conclusion, fter a careful inquiry into the geological formations of the 

 region and the sources of springs, that much water must lie, throughout 

 wide tracts, deep below the surface of the soil, and th:it the boring of 

 artesian wells would yield a permanent supply for irrigation. But as a 

 remedy for the growing evil, he laid particular stress on legislative enact- 

 ments to check reckless felling of timber and burning of pastures, which 

 had long been practised both by the natives and the European colonists. 

 Sir J. Alexander quoted instances to show how the destruction of 

 trees led to the desiccation of countries, especially in or near the tropical 

 zone. The protection of forests on hillsides, it was shown, had long been 

 part of the policy of the Indian Government. Capt. Jenkins cited, as 

 coming within his own experience, the instance of the arid territory of 

 the Imaum of Muscat, which in a few years, owing to the wise fore- 

 thought of the Imium in extensively planting cocoa-nut and date-palms, 

 had much increased in humidity and fertility, 



ON A CHANGE IN THE PHYSICAL CONDITION OF A COUNTRY 



CAUSED BY ANIMALS. 



In a paper read before the British Association, 1864, on the 

 country west of the Rocky Mountains, in British Columbia, along the 

 line of the Thompson River, by Dr. Cheadle and Viscount Milton, 

 the authors stated, that a great portion of the country to the cast of 

 the mountains was noticed to have been completely changed in char- 



A <-> 



acter by the agency of the beaver, which formerly existed here in 

 enormous numbers. The shallow valleys were formerly traversed by 

 rivers and chains of lakes which, dammed up along their course, at 

 numerous points, by the work of these animals, have become a 

 series of marshes in various stages of consolidation. So complete 

 has this change been, that hardly a stream is found for a distance of 

 200 miles, with the exception of the large rivers. The animals have 

 thus destroyed, by their own labors, the waters necessary to their ex- 

 istence. In the Thompson and Frazer river valleys, the travelers 

 noticed a series of raised terraces on a grand scale. They were 

 traced for 100 miles along the Thompson, and for about 200 miles 

 along the Frazer river ; forming three tiers on each side of the valley, 

 each tier being of the same hight as the corresponding one on the oppo- 

 site side. The lowest terrace was of great width and presented a per- 

 fectly level surface, raised some 30 or 40 feet above the water. The 

 second was seldom more than 100 yards wide, and stood at about 50 

 or 60 feet above the lower one. The third lay at a hight of 400 or 

 500 feet above the river on the face of the inaccessible bluffs. They 

 were all perfectly uniform and free from the rocks and boulders which 

 encumber the present bed of the river, being composed of sand, 

 gravel, and shale, the detritus of the neighboring mountains. The 

 explanation of these phenomena is to be sought in the barrier of the 

 lofty cascade chain of mountains, through which the Frazer has 



