37^ BULLETIN OF THE NEW YORK STATE MUSEUM 



limestones 2.70 to 2.76; the sandstones 2.48 to 2.75. The 

 absorptions percentage in the several classes is as follows : 



Granites 0.066-1 . 55. 



Marbles ... 0.08 -0.16. 



Limestones o . 07 -o . 14. 



Sandstones , ... 0.82-5.48. 



The greater absorbing capacity of the sandstones as com- 

 pared with the crystalline granites and limestones is appar- 

 ent in this table. And a granular structure is generally 

 more porous than a crystalline one, and less able to with- 

 stand the action of frost. "^ 



In the crystalline stones the structural arrangement is 

 important because of the diversity in the mineralogical spe- 

 cies. It may be well illustrated by reference to granite and 

 gneiss, which differ in the arrangement of the minerals 

 only. But this difference is a radical one in a consideration 

 of use as a building material. The parallel lines in the fo- 

 liated, gneissoid rocks, or the layers of feldspar, quartz and 

 mica, afford easy-splitting planes and ready access to moist- 

 ure. The rate of alteration and decay varies, and this un- 

 equal destruction of the mass lets down the more enduring 

 minerals and layers. Hence, as a rule, the granites are 

 more durable than the foliated rocks — as gneisses and 

 mica schists. The greater uniformity in the size of the 

 crystals also contributes to the strength of the stone. 



* The volume of water absorbed, when relatively large, increases the dampness, re- 

 quiring an increased consumption of fuel for its evaporation and, what is of far 

 greater importance, contributes to the injurious effects of alternations of heat and 

 cold, by freezing and thawing. In order to get a more impressive conception of the 

 amount of water which can be absorbed, assume the case of an ordinary brownstone 

 front. Then, given a height of fifty feet and a stone veneering eight inches thick, the 

 total weight of water which a saturated condition would represent in the several varie- 

 ties of sandstone, Potsdam, Medina, East Longmeadowand Connecticut brownstone, 

 would be as follows: 



Potsdam 1,685 pounds. 



Medina , 1,920 " 



East Longmeadow 4,255 " 



Portland, Connecticut 2,510 " 



or, in general, between three-quarters and two tons, nearly. 



