1883. 135 Trans. N. Y. Ac. Sa. 



the feldspar, the weakest constituent, remains with bright facets, with- 

 out change in color or lustre. It is by no means characteristic of the 

 " maladie du granit," first described by Dolomieu and later studied by 

 Dr. T. Sterry Hunt ; but here the action seems to be mainly and simply 

 a disintegration of the grains, initiated by expansion under the sun's 

 heat, during the summer, and developed by the expansion caused by 

 frost during the winter. An architect of the city recently stated that 

 '' he had built several large granite offices and co.isidered Quincy 

 granite the most durable of all building material. He thought the 

 weathering of granite would hardly amount to one-thirty-secondth of 

 an inch in a hundred years. According to that calculation many build- 

 ings might hope for a longer span than the thousand years spoken of 

 by the professor." 



However, it is a well-known fact that the weathering of granyte does 

 not proceed by a merely superficial wear, which can be measured or 

 limited by fractions of an inch ; but by a deep insinuation along the 

 lines of weakness, between grains, through cleavage-planes, and into 

 latent fissures. Thus, long before the surface has become much cor- 

 roded or removed, a deep disintegration has taken place by which large 

 fragments are ready for separation by frost, from the edges and argles 

 of a block. When directly exposed to the heat of the sun, an addi- 

 tional agency of destruction is involved, and the stone is suddenly 

 found ready to exfoliate, layer after layer, concentrically. As yet we 

 have little to guide us in the estimation of durability in years, since the 

 best known granyte monuments are those which have been exposed to 

 the exceptionally mild climate of Egypt ; but even there some exfolia- 

 tion has been noticed, e. ^., on the inner walls of the so-called Temple 

 of the Sphynx. 



In the cemeteries within the city and on Long Island, much granyte 

 is now used in slabs and monuments, but its introduction has been 

 everywhere of too recent a date to afford any measure of its durability. 

 Geikie remarks : " traces of decay in some of its feldspar crystals may 

 be detected, yet in no case that I have seen is the decay of a polished 

 granite surface sensibly apparent after exposure for fifteen or twenty 

 years. Even the most durable granite will probably be far surpassed 

 in permanence by the best of our silicious sandstones. But as yet the 

 data do not exist for making any satisfactory comparison between them," 



GNEISS. 



The oldest building in this city, in which this material has been used, 

 appears to be that of St. Matthews Lutheran Church, on the northeast 

 corner of Broome and Elizabeth streets, erected in 1841. The stone is 

 the micaceous gneiss, in part hornblendic, from excavations on the 



