1883. 75 Trans. N. V. Ac. Scf. 



to use for pavements, sidewalks, and stoops : the crystalline structure, 

 which, if well-developed, increases the strength of its resistance : the 

 tension of the grains, which appears to explain especially the disruption 

 of many crystalline marbles: the contiguity of the grains and the pro- 

 portion of cement in their interstices: and the homogeneity of the 

 rock. 



Again, the durability of a rock may depend upon the character of its 

 surface, whether polished, smoothly dressed, or rough-hewn, since 

 upon this circumstance may rest the rapidity with which atmos- 

 pheric waters are shed, or with which the deposition of soot, street- 

 dust, etc., may be favored : also upon the inclination and position of 

 the surface, as affecting the retention of rainwater and moisture, ex- 

 posure to northeast gales and to burning sun, etc. 



IV. Methods of Trial of Btcildins;- Stone. 



In such me:hods, two classes may be distinguished, the natural and 

 the artificial. 



The former embrace, first, the examination of quarry-outcrops, where 

 the exposure of the surface cf the rock during ages may give some in- 

 dication of its power of resistance to decomposition, e.s^., the dolomitic 

 marbles of New York and Westchester counties, some of which pre- 

 sent a surface crumbling into sand : and, secondly, the examination of 

 old masonry. P'ew old buildings have survived the changes in our 

 restless city, but many observations were presented in regard to the 

 condition of many materials, usually after an exposure of less than half 

 a century. 



Another source of information, in this regard, was found in the study 

 of the stones erected in our oldest cemeteries, e.g., that of Trinity 

 Church. There could hardly be devised a superior method for 

 thoroughly testing, by natural means, the durability of the stone, than 

 by its erection in this way, with partial insertion in the moist earth, 

 complete exposure to the winds, rain, and sun on every side, its bed- 

 ding-lamination standing on edge, and several of its surfaces smoothed 

 and polished and sharply incised with dates, inscriptions, and carvings,- 

 by which to detect and to measure the character and extent ot its 

 decay. In Trinity Church-yard, the stones are vertical, and stand 

 facing the east. The most common material is a red sandstone, pro- 

 bably from Little Falls, N. J., whose erection dates back as far as 1681, 

 and which remains, in most cases, in very fair condition. Its dark 

 color, however, has led to a frequent tendency to spli ting on the western 

 side of the slabs, i.e., that which faces the afternoon sun. Other 

 materials stud'ed consisted of bluestone, probably from the Catskills, 

 black slate, gray slate, green hydromicaceous schist, and white oolitic. 



