Trans. N. Y. Ac. Set. 138 May 7, 



on this important subject, and was sure that most of those in the 

 trade felt as he did. 



On invitation, Dr. T. Sterry Hunt observed that frost was the 

 main agent of the disintegration of stone in our climate, often 

 suddenly succeeding the moistening of the material by long rains, 

 and thus producing violent expansion and crumbling. In England, 

 no such extremes occurred. However, in visiting York Minster, 

 a few years ago, he found the workmen engaged in repairing the 

 magnesian limestone at one of the gates. He had climbed up the 

 ladder, and, on examination of the stone, found a remarkable dis- 

 integration near the middle, to the depth of one or two inches, by 

 which bars of the rock projected, marking the less absorbent layers. 



As to the granytes, that of Hallowell, Me., and that vicinity, is 

 only a granytoid gneiss, and not as compact as a true granyte ; its 

 exfoliation he knew to be a mere disintegration, favored by the 

 greater porosity of its texture. The material of the granyte obelisk 

 in Central Park is one likely to offer great resistance to disintegra- 

 tion and chemical decay, as the similar obelisks at Rome and Paris 

 seem to show little or no effect of weathering. 



The subject was further discussed by Messrs. Berg, Trotter, 

 and by the President, who expressed a cordial welcome to practical 

 men to attend the meetings of the Academy, and to contribute to 

 their interest through the valuable materials acquired by their ex- 

 perience. 



May 7, 1883. 



The President, Dr. J. S. Newberry, in the Chair. 



Thirty-three persons present. 



Mr. B. B. Chamberlin exhibited some curious concretions of 

 pyrite from the clay-pits at Amboy, N. J. They presented oval, 

 spherical, and sometimes annular forms, with radiated structure, 

 or with finely granular nuclei and beautifully crystallized envelopes. 



Prof. D. S. Martin remarked that similar concretions, some- 

 times exceedingly handsome and with curved crystals, occurred in 

 the white clay beds of New Jersey, belonging to the base of the 

 Cretaceous, and in the plastic clays of the same horizon, which may 

 perhaps represent the Wealden in this country. 



Tlie President stated that these specimens were certainly con- 



