Trans. N. V. Ac. Set. 126 Apr. 30. 



between 34th and 43d streets, etc.) the blackened discoloration and 

 frequent chipping of edges of the soft stone are quite offensive. On the 

 other hand, it must be admitted that a stone which cleans itself, by the 

 disintegration of its surface, the grains dropping out and so carrying 

 away the dirt, as in the poorer and softer varieties of brown-stone or of 

 Nova Scotia stone, is by that very action still more objectionable from 

 its want of durability ; and the discoloration of the Ohio stone is offset, 

 at least in part, in the best varieties, by their hardness and promise of 

 durability, 



Medma satidstone. — This material is of recent introduction {e. g.. 

 Baptist church on 57th street, west of 6th avenue), and its true dura- 

 bility cannot yet be estimated. 



Bluestone (graywacke). — This stone is yearly coming into more gen- 

 eral use, and, though somewhat sombre in tone and difificult to dress, 

 seems likely to prove a material of remarkable durability. In one 

 building in 24th street, between Madison and Fourth avenues, its con- 

 dition appears to be excellent, after fifteen years exposure, perfectly 

 retaining the tool-marks. The variety reported to come from the Wyo- 

 ming valley {e.g., in the building on the north side of Union Square) 

 is really derived, as I am informed by Prof. H. L. Fairchild, from 

 Meshoppen, Penn. 



In this connection, we may refer to the experiments made by Dr. 

 Hiram A. Cutting, of Vermont, on a series of American sandstones, in 

 regard to specific gravity, weight, absorptive power, and resistance to 

 fire. The results on varieties like those used in New York City are 

 quoted in the following table {The Weekly Underwriter, 1880, Vol. 

 XXII., p. 288) : 



