382 BULLETIN OF THE NEW YORK STATE MUSEUM 



CAUSES OF DECAY 



With Notes, of Observations 



The causes of decay have been noted incidentally in the 

 section on the durability of building stone. Their further 

 consideration may be illustrated by references to examples 

 in construction and to outcrops of rocks in which the phe- 

 nomena are well exhibited. 



The agents causing decay are physical and chemical. 



I. Physical Agents 



This group includes : 



1. Heat (and cold) — expansion and contraction. 



2. Mechanical abrasion, by water and by wind. 



3. Growing organisms. 



Climate and situation are factors of importance in a con- 

 sideration of the effects on building stone of variations in 

 temperature. In the dry air and less range of temperature 

 in Egypt, the coarse crystalline granite (syenite) retains its 

 smooth and even polished surface for centuries ; in our less 

 equable climate, and alternately dry and humid atmosphere, 

 the same stone scales after an exposure of a decade of years. 

 The marble structures of ancient Attica, the well-preserved 

 monuments of ancient Rome, in fact, of all the drier 

 climates of the Mediterranean basin, are, to-day, in so good 

 a state of preservation, not so much because of inherent 

 differences in the stone, or even in its use, as in the absence 

 of extreme degrees of frost. "^^ The situation, also, is of im- 



* The sculptured figures in the white, Pentelic marble of the columns and arches in 

 Rome are still well preserved, because of the pure and smokeless atmosphere as well 

 as by absence of extremes of temperature. — Hull, Building and Ornamental Stones 

 London, 1872, pp. 128-9. 



