General Strata. 365 



10. Calcjferous Sandrock, consists of fine grains of 

 quartzose sand and of carbonate of lime, united without cem- 

 ent, or with an exceeding small proportion. Subdivisions. — 

 Compact, when the rock is uniform, or nearly so, without 

 cells or cavities. Geodiferous, when it contains numerous 

 geodes, or curvilinear cavities ; which are empty or filled 

 with calc spar, quartz crystals,* barytes, anthracite, or other 

 mineral substances different from the rock. Varieties. — Oo- 

 litic, when it consists in part of oolite, of a dark color, and 

 harder than the kind which is common in the lias oolitic for- 

 mation of Europe. 



11. Metalliferous Limerock, consists of carbonate of 

 lime in a homogeneous state, or in the state of petrifactions 

 Subdivisions. — Compact, when it contains but few petrifac 

 tions, and is susceptible of a polish. Shelly, when it con 

 sists of petrifactions, mostly of bivalve molluscous animals 

 Variety. — Birdseye marble, when the natural layers are pierc 

 ed transversely with cylindrical petrifactions, so as to give 

 the birdseye appearance when polished. 



12. Second Graywacke, scarcely distinguished from first 

 graywacke, excepting by its relative position, being always 

 above calciferous sandrock. Subdivisions. — Compact, when 

 in blocks or slaty, consisting of fine grains. Rubble, when it. 

 consists of, or contains, large rounded pebbles. The rubble 

 of second graywacke is in a much smaller proportion than in 

 first graywacke. Varieties. — Red sandy, when it passes into 

 red sandstone, which formation occurs in a few localities. 

 Hone slate, when soft, and suitable for setting a fine edge. 

 Grindstone, when the quartzose particles are sharp-angular. 



Names under the Secondary Class. 



1 3. Millstone Grit, is a coarse, hard, aggregate of sharp- 

 angular quartzose sand or pebbles ; mostly without any cem- 

 ent, always grey or rusty grey. Subdivisions. — Sandy, when 

 it contains few or no pebbles. Conglomerate, when it con- 

 sists chiefly of rounded pebbles. 



14. Saliferous Rock, consists of red, or bluish-grey, 

 sand or clay-marle, or both. The grains of sand are mostly 



* On the north side of the Mohawk River, opposite to Spraker's Basin on the 

 Erie canal, hundreds of quartz crystals have been found in a ledge of this rock, 

 - containing anthracite coal. The crystals are mostly perfectly limpid, and have 

 pyramids at both ends ; but some are in limpid globules. 



