CAUSES OF DECAY 385 



of heat and cold in New York, has been the brownstone, and 

 mainly through improper position. The results are charge- 

 able to the architect and builder rather than to the stone. 



The crystalline rocks also suffer by frost, and reference 

 may be made again to the obelisk in New York, whence 

 have fallen many pounds of spalls or fragments forced off 

 by the frost.* 



Where the stone is homogeneous and close-grained, and 

 lacks the laminated or schistose structure, it Is better able to 

 resist disintegration by frost action. As already stated, the 

 greater the porosity and the more open-grained the stone, 

 the more water it can absorb, and the greater the force 

 which the frost can exert. It is however to be borne in 

 mind that a stone may be so coarse-grained and open as to 

 shed quickly its water and dry without damage from freez- 

 ing, as a sandy soil may dry sooner and not be frozen to the 

 depth of a clayey and compact layer. In our climate the 

 action of snow is apparently more damaging than rain, 

 as it facilitates the saturation of the stone, and the alterna- 

 tions of freezing and thawing are perhaps more frequent and 

 more severe. Especially is this the case near the ground, 

 and where the melting snow lies against the foundation. 

 In a higher and colder latitude, where the snow may act as 

 a protective covering against excessive cold, and the stone 

 be kept comparatively dry, except for a short period in the 

 spring and autumn, this action may be slight. As in the 

 case of wood the decay is most rapid near the water-line 

 and not under it ; so in that of stone, the greatest damage 

 is where there is the widest range and most frequent alter- 

 nation of heat and cold, and of wet and dry conditions. 



The mechanical abrasion by rain water is an effect which 

 cannot be measured in actual cases, but it is a factor in the 



* " So too, the obelisk of Luxor had stood for forty centuries in Egypt without being 

 perceptibly affected by that climate. * * * As the result of but forty years of 

 exposure (at Paris) it is now full of small cracks, and blanched, and evidently will 

 crumble to fragments before four centuries have passed." A. A. Julien, United States 

 Tenth Census, Vol. v, p. 370. 



49 



