No 104.] 189 



The same remarks hold true with regard to limestones ; and there 

 are few limestones that are not marked by partings of shale or clay, 

 which, in the course of time, weather into open seams, causing those 

 unsightly appearances so common in structures of this kind. 



In the granite and crystalline limestones, other causes, as the want 

 of cohesion among the particles, presence of destructive agents or 

 liability to chemical changes, and seams or patches of foreign matter, 

 are symptoms to be guarded against. It is not because a rock 

 offered as a building stone is a granite, a marhle, a limestone, or a 

 sandstone, that it is good or bad ; but this characteristic is to be 

 sought in other conditions, and the objectionable feature may be 

 accidental or adventitious. 



One other condition should be remembered. These materials 

 used for building are not promiscuously distributed over the country, 

 but are restricted to certain geological formations, and can only be 

 found within certain limits. Although we find granite, gneiss, and 

 various sienites, with crystalline limestone, in the mountainous 

 regions of Northern New York, it would be quite absurd to look for 

 rocks of this kind in the Catskill mountains. We find white and 

 variegated marbles in the region skirting the Highlands on the east, 

 and extending through Western Connecticut, Massachusetts and 

 Vermont ; but no well informed person expects this material in the 

 Helderberg mountains, or in the hills of the southern counties of 

 New York, Investigation has shown that certain kinds of rock, or 

 rocks of similar but very distinct characteristics, are confined to 

 certain geological formations, and do not occur out of these ; 

 and again, that these formations have certain limits which are already 

 defined and well understood. Geology has so well defined these 

 matters, and t'he association of certain rocks and minerals, that when 

 told that a known geological formation covers a portion of country, 

 we know what kind and character of rocks and other mineral pro- 

 ducts to expect. 



In a State where the geological structure is so well known as that 

 of New York, 1 think I may be allowed to speak of the various 

 building materials under the heads of the several geological forma- 

 tions to which they belong, or in which they occur; thus conveying 

 general information, while treating of the special suhject. 



All the Geanites, gYanitic, sienitlc, or gneissoid rocks of the 

 State are confined either to the northern portion, known as the 

 Adirondack region, from the name of the high mountain range in its 

 central part ; or to the Highland region along the Hudson river, 

 which is of the same geological age as the northern portion, and all 

 belonging to the Laurentian System. 



In the northern part of the State, Crystalline limestone, of 

 various colors, is associated with granitic or gneissoid rocks ; the 

 same is true, in a less degree, of the granitic region of the High- 

 lands. 



The White and Yakiegated Marble§, so much in general use, 

 belong to a different geological age and constitute a distinct belt of 



