220 ANNUAL OF SCIENTIFIC DISCOVERY. 



Striation, read before the Geological Section of the British Associ- 

 ation, 18(55.) 



Whether the height of a crushing column of ice be 710 or 

 1,000 or 1,500 feet is of no consequence whatever as regards the 

 possible thickness of a glacier. No doubt a piece of ice solidified 

 under no pressure would be crushed to powder were it placed 

 under a glacier 1,000 feet in thickness or so; but after being 

 crushed, it would resolidify, and would then probably be able to 

 sustain a pressure of 2,000 feet of ice. This follows as a necessary 

 consequence from the property of regelation. There is as yet, 

 so far as I am aware, no known limit to the amount of pressure 

 which tee can sustain. There probably is a limit; but what that 

 limit is has not yet been determined. Canon Mosely says that 

 " There is no glacier alleged to have so great a depth as 710 feet." 

 The Humboldt glacier in North Greenland, according to Dr. 

 Kane, has a depth of more than three times 710 feet. Dr. 

 Hayes found in Baffin's Bay icebergs (which are just pieces 

 broken off the ends of glaciers) aground in about half a mile of 

 water, while on the Antarctic continent we have reasons for 

 believing that the ice is in some places over a mile in thickness. 

 J. Croll. Amer. Jour. Science, from Geological Magazine for 

 June, 1870,p. 276. 



THE DESCENT OF GLACIERS. 



Do Saussure, who was the first to study with care the descent of 

 glaciers, held that glaciers slip down the slopes on which they 

 rest as any other body would slip down an inclined plane. As 

 soon, however, as it appeared that the glacier did not move 

 forward as a body, but that different portions of the mass moved 

 with different velocities, there was propounded the viscous theory, 

 which supposed the ice to be a fluid, and not the solid thing it 

 seems to be. This theory was ably advocated by the late Prin- 

 cipal James Forbes. The experiments of Faraday and Tyndall 

 led to the regelation theory, which supposes that by the pressure 

 exerted from behind the ice is crushed through and over the 

 irregularities of its course, and is united again by pressure to a 

 homogeneous mass. 



In regard to this subject of the descent of glaciers, Canon 

 Moseley says: "At this stage the question had assumed this new 

 form. If ice be a viscous fluid, according to the viscous theory, 

 is it fluid enough to descend by its own weight; or, if it be solid, 

 according to the regelation theory, is it little enough solid so to 

 descend? 



" If, instead of ice, a glacier were of water, it would obviously 

 descend by its weight. The same would be true if it were of 

 oil, or soft mud, or quicksilver, or probably of pitch ; but if it 

 were of iron, or of copper, or of lead, it would not descend by its 

 weight only, unless, indeed, these metals were in a state of fusion. 

 A quicksilver glacier would descend by its weight only, because it 

 shears easily ; a cast-iron one would not, because it shears with 

 diiliculty. There must, therefore, exist a relation between the 



