8 Report on Building Stone of New York. 



daga gray limestone, the Potsdam sandstone, the Oneida conglomerate 

 and the Medina sandstone are nearly as well known and as readily 

 recognized by the practical quarrymen as by geological experts. 

 And in the State the outcrops of these formations are to some 

 extent natural divisions, whose topography and general surface char- 

 acters are due to these rocks. Hence in the geographical distribution 

 of the several kinds of rock or stone, the limits are determined by the 

 extent of the geological formations. And a geological map of the 

 State shows where they may be found. 



The arrangement, as indicated above, is into the following kinds of 

 rock and the geological groups to which they belong : 



Kinds of Rock. 



I. Crystalline Rocks. 



1. Granites, syenites, gneisses, mica schists. 



2. Trap-rocks. 



3. Marbles, serpentines. 



II. Sub-crystalline and Fragmental Rocks.* 



1. Quartzytes and sandstones. 



2. Limestones. 



3. Slates. 



The rocks of the sub-crystalline and fragmental division are sub- 

 divided and arranged in the following geological groups : 



Sandstone. 



Potsdam. 



Hudson River group. 



Medina. 



Clinton group. 



Hamilton. 



Portage. 



Chemung. 



Catskill. 



New Red Sandstone. 



Limestones. 



Calciterous. 

 Chazy. 

 Trenton. 

 Niagara. 



Lower Helderberg. 

 Upper Helderberg. 

 Tully Limestone. 



* Many of the rocks in this second general head are crystalline or sub-crystal- 

 line ; but as the structure in nearly all cases is not recognizable by the unaided 

 eye, the division is consistent with practice and is retained. The strictly fragmental 

 rocks are slates, Bandstonea and conglomerates. Building stones are sometimes 

 classified as crystalline, sedimentary and calcareous rocks. 



