572 THE POPULAR SCIENCE MONTHLY 



ing and organic modifications of the " drift." The drainage has been 

 greatly interrupted, and new channels, waterfalls and lakes abound. 

 Several types of hills of accumulation appear that we can not find in 

 the southern mountains. The tops of hills and mountains of hard rock 

 have a different aspect — it is the product of the glacial cycle which we 

 are contemplating, and the geographer would only need to cast his eye 

 upon maps of the two regions to recognize their character. 



Let us go to the Great Basin. Bather is it a group of basins, 

 flanked by the Wasatch on the east and the Sierras on the west. Its 

 broad and arid expanse is intersected by many north and south moun- 

 tain ridges, which are the up-thrown edges of great crustal blocks. The 

 upper parts of these mountains show normal erosion. The bordering 

 Sierras show normal and glacial types. Within the basin the summits 

 and slopes of the mountain are shedding down their waste and streams 

 of greater or less vigor are carving a normal topography. At the foot 

 of the mountains, the waste, instead of going in the grasp of streams 

 to the sea, is spread out on the inter-montane floors, raising the surface 

 and building plains of sand, clay, salt and gypsum. The rivers become 

 small instead of growing, and lose themselves in the atmosphere, the 

 soil and in shallow lakes which may be permanent and salt, or inter- 

 mittent and brackish. The soil is formed mechanically and with but 

 a minor amount of those chemical changes which take place in a more 

 humid climate. Vegetation is scant and this condition retards true 

 soil-making and, by lack of cover, aids the action of winds. Monotony 

 characterizes the arid type, as ceaseless variety belongs to the normal 

 and glacial operations. The ridges that separate adjacent arid basins 

 may be cut away, and both be merged in a single featureless plain, and 

 thus we have a growing lake of waste, somewhat akin to closed basins 

 of water. The only means by which such a basin can lose its material 

 is through the winds. Central Persia offers another land of the same 

 order, where severe conditions of aridity have for an unknown period 

 reflected themselves in the life of man and in the very forms of the 

 land which he makes his home. 



Hill and mountain, valley and plain, thus own their dependence, 

 in no remote way, upon the gaseous envelope. As it is wet or dry, hot 

 or cold, so evolves the very physiognomy of our globe, and whether we 

 cross the border of an adjacent township or journey to a far country, 

 its handiwork is before our eyes. 



No forms are more characteristic or interesting than those which 

 the ocean makes on its borders. These forms in a minor way are due 

 to the tides, in the major way to waves, and thus, at one remove only, 

 are produced by the atmosphere. Likewise ocean currents, involving 

 transfers of heat, moisture, plants and animals, are believed to be 

 chiefly due to atmospheric movements. If we compare New York with 

 Rome and Constantinople, or Labrador and Hudson Bay with Great 



