8o 



The National Geographic Magazine 



" Development and application of 

 Water near San Bernardino, Colton, and 

 Riverside, California," by J. B. Lippin- 

 cott, resident hydrographer for the State 

 of California. Mr Lippincott presents 

 some striking instances of what may be 

 done by irrigation. On land that fifteen 

 years ago was worth barely 75 cents an 

 acre as a sheep pasture now flourish, as 

 a result of irrigation, orchards of orange 

 and citrous trees yielding a net revenue 

 of $100 an acre. 



"Sewage Pollution in the Streams 

 Adjacent to New York City," by Mar- 

 shall O. Leighton; a discussion of the 

 incalculable damage to property along 

 the Passaic River of New Jersey, and 

 along the streams flowing into the upper 

 Hudson by discharge of city sewage. 



' ' The Possibilities of Increasing the 

 Water Supply of Central Washington," 

 by F. C. Calkins, of the hydrographic 

 division of the Survey. 



' ' Geology of the Globe Copper Dis- 

 trict, Arizona," by Dr Frederick L. 

 Ransome. 



TIMBER LINES 



AN interesting paper on ' ' Timber 

 Lines ' ' was presented by Prof. 

 Israel C. Russell to the recent meeting 

 in Washington, D. C, of the Gelogical 

 Society of America. The following is 

 an abstract of the address : 



"'Timber line,' as commonly de- 

 fined, is the upper limit of arboreal veg- 

 etation on mountains. Its position is 

 determined mainly by the occurrence of 

 a mean annual temperature of about 32 

 degrees Fahrenheit, but locally its ele- 

 vation is regulated by soil conditions 

 and by differences between various lo- 

 calities in snow-fall, severity of winter 

 storms, exposure to the sun, etc. It 

 may with propriety be termed the ' cold 

 timber-line.' Above it on high moun- 

 tains there is commonly a region occu- 

 pied by alpine flowers, and still higher 

 a region of perpetual snow. When 



traced from warm to colder regions or, 

 in general, from the equator toward 

 either pole, it becomes lower and lower. 

 In North America it descends nearly to 

 sea-level in Alaska and northern Can- 

 ada, where it defines the northern limit 

 of the subarctic forest and becomes the 

 ' continental timber-line, ' to the north 

 of which lie the barren grounds and 

 tundras, which correspond to the zone 

 of alpine flowers on lofty mountains in 

 temperate latitudes. 



' ' On some of the mountain ranges of 

 the arid portion of the United States 

 there is a lower limit of tree growth, 

 the position of which is determined in 

 the main by insufficient moisture, and 

 locally by soil conditions, including the 

 presence of alkali, hot winds, forest 

 fires, exposure to the sun, etc. This 

 may be termed the ' dry timber-line' . 

 Below it are treeless, grass-covered 

 plains and valleys. On the mountains 

 of central Idaho, the cold timber-line is 

 sharply drawn at an elevation of about 

 10,000 feet, while the dry timber-line, 

 equally well defined, has an elevation 

 of about 7,000 feet; between the two 

 there is a belt of forest trees which en- 

 circles the mountains. In southeastern 

 Oregon, Nevada, southern California, 

 etc., where the climate is excessively 

 arid, the dry timber-line is higher than 

 in Idaho, and in certain localities meets 

 the cold timber-line, and the mountains 

 are bare of trees from base to summit. 

 The dry timber-line decreases in ele- 

 vation when traced from arid to humid 

 regions. In the central part of the con- 

 tinental basin of North America, it de- 

 fines the border of the treeless portion 

 of the Great Plateaus and the prairie 

 plains, and at the north coincides with 

 the southern limit of the subarctic 

 forest. On the borders of the treeless 

 plateaus and the prairie plains the posi- 

 tion of the margin of the encircling 

 forest is determined mainly by lack of 

 moisture, but is varied locally by soil 

 conditions, hot winds, forest fires, etc., 



