208 [Assembly 



ers of the stone which have been broken off, and are more or less 

 driven forward into the softer parts. In looking at similar surfaces 

 which have been a long time exposed to the weather, it will be seen 

 that the stone adjacent to the seam presents an interrupted fractured 

 margin; the small fragments having dropped out in the process of 

 weathering. Limestones of this character are much better adapted to 

 rough dressing, when the blows are directed away from the surface 

 instead of against it, and when the entire surface shall be left of the 

 natural fresh fracture. By this process the clay seams have not been 

 crushed, nor the limestone margining them broken, and the stone 

 withstands the weather much longer than otherwise. The attempt at 

 fine hammer-dressing is injurious to any stone; for the cohesion of the 

 particles is necessarily destroyed, and a portion of the surface left in a 

 condition to be much more readily acted upon by the weather. 



The gray, sometimes brownish-gray, subcrystalline limestone, which 

 is not metamorphic, is usually composed of fragments of organic 

 remains more or less comminuted, with the interstices filled with fine 

 particles of the same, or with an impalpable calcareous mud. In such 

 rocks, the fragmentsof fossils being crystalline, withstand the weather- 

 ing action, while the intermediate portions wear away, leaving a rough 

 and sometimes unsightly surface. The disintegration from this cause 

 is slow ; and in the absence of clay seams, a structure of this kind of 

 stone may remain a long time without material deterioration. 



One of the best limestones of this character, and perhaps the best in 

 the country in relation to freedom from clay seams, is the encrinal lime- 

 stone of Lockport, which, at that point, constitutes a portion of the lower 

 part of the Niagara limestone. The Onondaga limestone, in the quar- 

 ries south of Syracuse, is one of the most useful and serviceable of 

 these limestones, and when free from clay seams, is equal to any other 

 limestone in color, quality and durability. In some portions of the 

 Onondaga beds to the westward, and in some similar beds of gray lime- 

 stone in the Lower Helderberg group, the mass requires firmness; and 

 the want of compactness or close coherence among the particles allows 

 the infiltration of water, which, charged with carbonic acid, acts still 

 further to lessen their cohesion. 



In some of the Lower Silurian limestones, the entire mass of the 

 dark-colored beds is completely penetrated by irregular ramifications 

 of siliceous matter, which, in their position and relations, seem 

 as if they may have been fucoidal or spougoid bodies growing 

 upon the bottom at the time of the deposition of tlie calcareous de- 

 posits. The beds of this character furnish a strong and durable material 

 for rough masonry and foundations, and some of the beds bear dress- 

 ing with satisfactory results. 



In the process of metamorphism, the limestones have become more 

 or less changed to a white, bluish or grayish-white color, or to varie- 

 gated white and gray. The seams of argillaceous matter which mark 

 the line of bedding in ordinary limestones have undergone some chem- 

 ical change, and have become chloritic, talcose or micaceous, of a 

 greenish, bluish or variegated color, but nevertheless still retaining the 

 same relations to the calcareous part of the mass as in their normal 

 condition. Although they are no longer a clay or shale, but have under- 

 gone some chemical change, these parts are nevertheless usually softer 

 and weather more rapidly thg-n the surrounding calcareous portions ; or 



