DISINTEGRATING WORK OF FREEZING WATER. 441 



As shown by Buckley," the efficiency of the change of water to ice in 

 disintegrating the rocks is largely dependent upon the readiness with 

 which the water from a saturated rock can escape. If the pore spaces are 

 large and continuous, as in sandstones, even where the rocks have been 

 recently saturated, as by a heavy rain, a large part of the water readily 

 and quickly escapes, so the water held long enough to freeze is mainly 

 that which adheres to the grains or is the water of imbibition. If the pore 

 spaces are not nearly full when the small amount of water is frozen 

 there is room for expansion without disrupting the grains, and consequently 

 there is very little effect in the way of disintegration. Hence a very porous 

 rock where drainage is easy may be comparatively little affected by 

 repeated freezing and thawing. On the other hand, if a rock be fine 

 grained, so that the pore space, while of the same volume as in a sandstone, 

 is very much subdivided, the water of imbibition and that of saturation 

 approximate to each other; the water escapes much more slowly; the pore 

 spaces may be nearly full for some time, and freezing is therefore much 

 more likely to disintegrate the rock. Such rocks are illustrated by the 

 chalks. 



Further, in rocks which have a very small amount of pore space, and 

 in which the pore spaces are more or less discontinuous or are subcapillary, 

 so that the water is held firmly, the destructive effect of the freezing of the 

 small amount of water may be very great, because the pore sj)ace is full 

 and expansion must cause disruption. 



The relation of size and continuity of pore space to disintegration by 

 freezing is well illustrated by the resistance of sandstones as compared with 

 granites and limestones. The DunnVille sandstone of Wisconsin has the 

 remarkably large pore space of 28 per cent. Buckley repeatedly saturated 

 specimens of this stone with water and immediately exposed them to tem- 

 peratures below 0° C, but the water so rapidly escaped that the strength 

 of this rock was "proportionally less affected by freezing and thawing than 

 the strong granites and limestones, having low percentages of j)ore space." 6 

 In contrast with this is the behavior of Cleopatra's Needle, a granite mon- 

 olith in Central Park, New York, which, after having- resisted for thousands 



"Buckley, E. R., Building and ornamental stones: Bull. Wisconsin Geol. and Nat. Hist. Survey 

 No. 4, 1898, p. 382. 



^Buckley, cit., p. 382. 



