O- IE IN" IE IR, .A. L 



Classification and Arrangement. 



Any division of the building stones (or stone used in construction), 

 which occur naturally, is to some extent arbitrary. The basis for it 

 may be in the nature of the rock as to its constituent minerals, their 

 arrangement and their relative proportion in the mass, or it may be 

 in the formation, or geological horizon whence it comes. The latter 

 has regard to the source rather than the nature or kind of rock. 

 Thus granites and gneisses differ in the arrangement of the minerals 

 which make up the rock or stone and not, necessarily, in the minerals 

 or even in their chemical composition. Again, for example, lime- 

 stones and marbles differ in the degree of crystallization and not 

 in chemical composition. Then, again there are sandstones, slates, 

 serpentines and trap-rocks, classes which differ mineralogically and 

 chemically. From the stand point of geology the natural building 

 stones may belong to widely different geological formations or ages 

 and yet in their composition be almost identical. Saudstones and 

 limestones especially are widely represented in the various formations. 

 Marble may come from the oldest or Archaean or from the Silurian 

 or from the later geological rock outcrops. In our own State the 

 Tuckahoe and Sing Sing marbles, the coral-shell marble of Hudson, 

 the Glens Falls black marble and the Lockport marble are represen- 

 tatives of different geological epochs. And the so-called granites 

 comprehend rocks, which differ in their mineralogical constitution 

 and in the formation to which they belong. The division or arrange- 

 ment, which is indicated by the geological age is, therefore, not so 

 natural or definite as the former. But it is serviceable in a secondary 

 division or subdivision of the classes, which rest upon mineral 

 differences. 



The best classification is, primarily into the kinds of rock or stone, 

 and, secondarily, into groups corresponding to the several geological 

 formations. The first are fully recognized in the practical and busi- 

 ness circles ; the geological grouping also is known, but is not so 

 generally appreciated and understood. In New York the characters 

 of some of the geological subdivisions have been so carefully studied 

 as to become well known, and they are so persistent that they are 

 types. The Black River limestone, the Trenton limestone, the Onon- 



