Geography of Ohio 189 



of pressure. It has been determined that when the pressure 

 evolved in a growing mass of ice equals one atmosphere, the heat 

 equivalent is to 0.0075° C. Students now believe that in masses 

 of ice, either of the Alpine or Continental glacier type, there is 

 constant melting and almost immediate refrigeration of tiny 

 particles of ice and water, resulting possibly from pressure and 

 constant tension. If this is true, the units, either crystals or 

 granules, in an ice sheet must be almost constantly in motion. 



At the heads of glaciers, where motion is initiated, there may ])e 

 great downward pressure, ])ut not vigorous thrusts from behind, and 

 probably only moderate thrusts developed within the body itself. There 

 seems, therefore, no escape from the conclusion that the primal cause 

 of glacial motion is one which may operate even under the relatively 

 low temperatures, the relatively dry conditions, and the relatively granu- 

 lar textures which affect the heads of glaciers. These considerations 

 lead to the view that movement takes place by the minute individual 

 movements of the grains upon one another. While they are in the spher- 

 oidal form, as in the neve, this would not seem to be at all difficult. They 

 may rotate and slide over each other as the weight of the snow increases; 

 but as they become interlocked by growth, both rotation and sliding 

 must apparently encounter more resistance. Th(> amount of rotary 

 motion required of an individual granule is, however, surprisingly 

 small, and the meltings and refreezings incident to shifting pressures and 

 tensions, and to the growth of the granules, seem ackHjuate to meet the 

 requirements. In order to account for a movement of three feet per day 

 in a glacier six miles long, the mean motion of the average granule rela- 

 tive to its neighbor would be, roundly, looutt of its own diameter per 

 day, or one diameter in 10,000 days; in other words, it would change its 

 relation to its neighbors to the extent of its diameter in al)out thirty 

 years. A change of so great slowness under the conditions of granular 

 alteration can scarcely be thought incredible, or even improbable, in 

 spite of the interlocking which the granules nuiy develop. The move- 

 ment is supposed to be permitted chiefly by the temporary passage of 

 minute portions of the granules into the fluid form at the points of great- 

 est compression, the transfer of the moisture to adjoining points, and its 

 resolidification. The points of greatest compression are obviously just 

 those whose yielding most promotes motion, and a successive yielding 

 of the points that come in succession to oppose motion most (and thus to 

 receive the greatest stresses) permits continuous motion. It is merely 

 necessary to assume that the gravity of the accumulated mass is sufficient 

 to produce the minute temporary liquefaction at the points of greatest 

 stress, the result being accomplished not so much by the lowering of the 

 melting-point as by the development of heat by pressure. 



This conception of glacial "flowage" involves only the momentary 

 liquefaction of minute portions of the mass, while the ice as a whole 



