283 



SCIENTIFIC SIDE-LIGHTS 



Gfaciers 



of water constantly flowing in is very great, 

 and there is only one cause to which this 

 can be attributed, the loss of water in the 

 Mediterranean by evaporation. That the 

 level of this sea should be considerably de- 

 pressed by this cause is quite conceivable, 

 since we know that the winds blowing from 

 the shores of Africa are hot and dry; and 

 hygrometric experiments recently made in 

 Malta and other places show that the mean 

 quantity of moisture in the air investing 

 the Mediterranean is equal only to one-half 

 of that in the atmosphere of England. The 

 temperature also of the great inland sea is 

 upon an average higher, by 3y 2 of Fahren- 

 heit, than the eastern part of the Atlantic 

 Ocean in the same latitude, which must 

 greatly promote its evaporation. The Black 

 "Sea being situated in a higher latitude, and 

 being the receptable of rivers flowing from 

 the north, is much colder, and its expendi- 

 ture far less; accordingly it does not draw 

 any supply from the Mediterranean, but, on 

 the contrary, contributes to it by a current 

 flowing outwards, for the most part of the 

 year, through the Dardanelles. The dis- 

 charge, however, at the Bosporus is so 

 small, when compared to the volume of 

 water carried in by rivers, as to imply a 

 great amount of evaporation in the Black 

 Sea. LYELL Principles of Geology, bk. ii, 

 ch. 20, p. 333. (A., 1854.) 



1377. GLACIER CHANGING SHAPE 



Fracture and Regelation. All the phenom- 

 ena of motion, on which the idea of viscos- 

 ity [a view still held by eminent observers, 

 as at least a partial explanation of glacial 

 phenomena see Russell, " Glaciers of North 

 America "] has been based, are brought by 

 such experiments as the above [of breaking 

 and freezing together the fragments of ice] 

 into harmony with the demonstrable prop- 

 erties of ice. In virtue of this property, the 

 glacier accommodates itself to its bed while 

 preserving its general continuity, crevasses 

 are closed up, and the broken ice of a cas- 

 cade, such as that of the Talefere or the 

 Rhone, is recompacted to a solid continuous 

 mass. TYNDALL Hours of Exercise in the 

 Alps (Notes on Ice and Glaciers), ch. 1, p. 

 355. (A., 1898.) 



1378. GLACIER, DISTINCTIVE CARV- 

 ING OF Markings Could Not Be the Work of 

 Floating Ice. In the State of Maine I have 

 followed, compass in hand, the same set of 

 furrows, running from north to south in 

 one unvarying line, over a surface of one 

 hundred and thirty miles, from the Katah- 

 din Iron Range to the seashore. These 

 furrows follow all the inequalities of the 

 country, ascending ranges of hills varying 

 from twelve to fifteen hundred feet in 

 height, and descending into the intervening 

 valleys only two or three hundred feet above 

 the sea, or sometimes even on a level with 

 it. I take it to be impossible that a float- 

 ing mass of ice should travel onward in one 

 rectilinear direction, turning neither to the 



right nor to the left, for such a distance. 

 Equally impossible would it be for a de- 

 tached mass of ice, swimming on the surface 

 of the water, or even with its base sunk con- 

 siderably below it, to furrow in a straight 

 line the summits and sides of the hills, and 

 the bottoms of the intervening valleys. It 

 would be carried over the inequalities of 

 the country without touching the lowest 

 depressions. AGASSIZ Journey in Brazil, 

 ch. 13, p. 402. (H. M. & CD., 1896.) 



1379. GLACIER OF CONTINENTAL 

 MAGNITUDE Greenland a Type of Ancient 

 North America. The vast ice-sheet cov- 

 ering nearly all of Greenland is of the 

 continental type, and,, as is well known, is 

 the largest existing ice-body in the northern 

 hemisphere. Its extension northward has 

 not been fully determined, but as nearly 

 as can be judged it terminates in about 

 latitude 82. Its area is in the neighbor- 

 hood of 600,000 square miles. If trans- 

 ferred bodily to the eastern portion of the 

 United States, it would extend from north- 

 ern Maine to Georgia, and cover a belt of 

 country 500 miles broad. Vast as this ice- 

 sheet is known to be, it takes what may 

 be said to be second or third rank when 

 contrasted with the continental glaciers that 

 occupied Canada and a large portion of the 

 United States in Pleistocene times. The 

 exploration of existing glaciers derives one 

 of its principal attractions from the fact 

 that such studies assist in interpreting the 

 records left by ancient glaciers in various 

 parts of the world. This in turn brings one 

 to the consideration of the still broader 

 problems of the cause of climatic changes 

 which favored the growth of vast Pleisto- 

 cene glaciers in regions now enjoying a tem- 

 perate climate, and inhabited by the most 

 civilized people of the earth. RUSSELL Gla- 

 ciers of North America, ch. 2, p. 35. (G. & 

 Co., 1897.) 



1380. GLACIERS, FORMING AND 

 MOVEMENT OF Rivers Flowing Under 

 Arches of Ice. In the temperate zone the 

 snow lies for months in winter on the sum- 

 mit of every high mountain, while in the 

 arctic regions a long summer's day of half 

 a year's duration is insufficient to melt the 

 snow, even on land just raised above the 

 level of the sea. It is therefore not sur- 

 prising, since the atmosphere becomes colder 

 in proportion as we ascend in it, that there 

 should be heights, even in tropical countries, 

 where the snow never melts. The lowest 

 limit to which the perpetual snow extends 

 downwards from the tops of mountains at 

 the equator is an elevation of not less than 

 16,000 feet above the sea; while in the Swiss 

 Alps, in lat. 46 N., it reaches as low as 

 8,500 feet above the same level, the loftier 

 peaks of the Alpine chain being from 12,000 

 to 15,000 feet high. The frozen mass aug- 

 menting from year to year would add in- 

 definitely to the altitude of Alpine summits 

 were it not relieved by its descent through 



