454 REPOET ON NATIONAL MUSEUM, 1886. 



SO pronoiiuced as to be readly recognized thereby. The lirst of these 

 belong to the IJamilton period of the Devoniau Ibrinations, and are 

 fine-grained, compact, dark bhie-gray stones, very strong and durable.* 



They give a pronounced clayey odor when breathed upon, and have 

 been desigiviited grey wade by Professor Jnlien, though j^opularly known 

 as "bluestones " for their ordinary color. The second group belongs to 

 the Medina period of the Upper Silurian formations. These stones are 

 largely siliceous, of coarser, more distinctly granular texture than the 

 last, and are of a gray or red color. The third and last group belongs 

 to the Potsdam period of the Cambrian formations. Like the Medina 

 stone, they are largely siliceous, and contain a much larger proportion 

 of siliceous cementing material. These are usually light red or nearly 

 white and intensely hard and refractory. 



Discussing each gr.oup more in detail, it may be said that the -'blue- 

 stone" district is confined to comparatively narrow limits west of the 

 Hudson Eiver, and mainly to Albany, Green, and Ulster Counties. It 

 begins in Schoharie County, passes to the southeast and enters Albany 

 County near Berne, and from there passes around to the south and south- 

 west across Green, Ulster, and Sullivan Counties, and across the west 

 end of Orange County to the Delaware Eiver and into Pike County, 

 Pennsylvania.! 



The typical bluestone belongs to the Hamilton period, and is a fine- 

 grained, compact, tough, and eminently durable rock of a deep dark blue- 

 gray color. Owing to the fact that it occurs usually in thin beds and 

 splits out readily in slabs but a few inches thick, it has ])een used very 

 extensively for flagging, curbs, sills, caps, steps, etc. Its somber color is 

 something of a drawbacK to its use for general building iKirposes. As a 

 rule the quarries are shallow affairs, and the work carried on in the 

 crudest possible methods. At Quarryville, Ulster County, the quarries 

 have been worked for upwards of forty years, and vast quantities of the 

 mater-ial removed. The quarries lie in lines along three i)arallel ledges, 

 which have a general northeast and southwest direction, the beds of 

 sandstone overlying each other from west to enst, with strata of slate 

 aud hard sandstone between them. The quarries in the easternmost 

 ledge extend about a mile in length, 175 feet in width, and have been 

 worked to an average depth of about 12 feet. In the middle ledge the 

 line of quarries extends over an area about 1^ miles in length, 150 to 

 500 feet in width, and have been quarried to a depth of from 12 to 20 



* Microscopic examination lias sliown the Devonian sandstones of New York to 

 consist chiefly of "angular to suban^nlar grains of quartz and feldspar, with their 

 interstices occupied by smaller grains of magnetite, scales of chlorite, and particu- 

 larly short iibers of hornblende interlacing the grains of the other constituents. The 

 result is an ' argillaceous sandstone,' flagstone, or greywacke, peculiarly comijact 

 and impermeable, which has retained its fresh condition to an extent which could 

 not otherwise have been expected from an aggregate so liable to ready decomposi- 

 tion." A. A. Julien in Proc. A. A. A. S., Vol. xxviii, 1879, p. 372. 



t Report of the Tenth Census, Vol. x, 1880, p. 130. 



