MECHANICAL ACTION OF WATEE AND ICE 177 



such size as to be lifted or moved by wave action, but too heavy 

 to be protected from attrition by the thin film of water above 

 alluded to. Shaler's observations^ at Cape Ann were to the 

 effect that ordinary granitic paving blocks (weighing perhaps 

 twenty pounds) were, when exposed to surf action, worn in the 

 course of a year into spheroidal forms such as to indicate an 

 average loss of more than an inch from their peripheries. Even 

 the crystallization of the salt thrown up by wave action and ab- 

 sorbed into the pores of rocks serves in its way the purposes of 

 disintegration.^ 



The Action of Freezing Water and of Ice. — The action of 

 dry heat and cold in disintegrating rocks has already been 

 described. The effects of such temperature changes upon 

 stone of ordinary dryness are, however, slight in comparison 

 with the destructive agencies of freezing temperatures upon 

 stones saturated with moisture. The expansive force of water 

 passing from the liquid to the solid state has been graphically 

 described as equal to the weight of a column of ice a mile high 

 (about 150 tons to the square foot). Otherwise expressed, 100 

 volumes of water expand, on freezing, to form 109 volumes of 

 ice. Provided, then, sufficient water be contained within the 

 pores of a stone, it is easy to understand that the results of 

 freezing must be disastrous. That stones as they lie in the 

 ground do contain moisture, often in no inconsiderable amounts, 

 is a well-known and well-recognized fact by all those engaged 

 in quarrying operations, and indeed no mineral substance is 

 absolutely impervious to it. The amount contained, naturally 

 varies with the nature of the mineral constituents and their 

 state of aggregation. According to various authorities, granite 

 may contain some 0.37% by weight; chalk, 20%; ordinary 

 compact limestone, 0.5% to 5% ; marble, about 0.30% ; and 

 sandstones, amounts varying up to 10% or 12%, while clay 

 may contain nearly one-fourth its weight. This water is largely 

 interstitial — the quarry water, as it is sometimes called. In 

 addition to this, the quartz, particularly of granitic rocks, almost 

 universally contains minute cavities partially filled with water, 



^ Bull. Geol. Soc. of America, Vol. V, p. 208. 



2 Aeeorcling to Dana (Wilkes' Exploring Expedition, Geology, p. 529), the 

 sandstones along tlie coast of Sydney, Australia, are subjected to a mechani- 

 cal disintegration through the crystallization of salt which is absorbed from 

 the saline spray of the ocean waves, 



13 



