74 LITHOLOGICAL GEOLOGY. 



(5.) Jasper Rock. — A flinty siliceous rock, of dull red, yellow, or green color, or 

 some other dark shade, breaking with a smooth surface like flint. It consists of quartz, 

 with more or less clay and oxyd of iron. The red contains the oxyd of iron in an an- 

 hydrous state, the yellow in a hydrous; on burning the latter, it turns red 



(6.) Buhrstone. — A cellular siliceous rock, flinty in texture. It is used for mill- 

 stones. Found mostly in connection with Tertiary rocks, and formed apparently from 

 the action of siliceous solutions on preexisting fossiliferous beds. 



8. Iron-Ore rocks. 



Specular Iron-Ore {Hematite) and Magnetic Iron-Ore occur 

 as rocks of considerable thickness among the rnetamorphic rocks, 

 especially the hornblendic and chloritic kinds. There are schistose or 

 laminated as well as massive varieties. These iron-ore beds occur 

 extensively in northern New York, Canada, Michigan, and Missouri; 

 in New Jersey and North Carolina : also in Sweden and elsewhere. 

 Their alternation, in these regions, with chloritic and other schists 

 and gneissoid rocks shows that they are metamorphic as well as the 

 schists. Devonian strata full of fossils, in Nova Scotia, at Moose 

 River, contain a bed of magnetic iron ore ; and at Nictaux, a bed six 

 feet thick of hematite. (Dawson.) Titanic iron-ore occurs in great 

 beds of like extent in Canada, and is mixed with the magnetite of 

 northern New York and western North Carolina. (See p. 154.) 



Franklinite, an iron-zinc ore, is also one of the metamorphic rocks in northern New 

 Jersey. 



3. Calcareous Rocks. — Carbonates and Sulphates. 



(1.) Massive Limestone. — - Uncrystalline Limestone. — Most lime- 

 stones have been formed from shells and corals ground up by the action 

 of the sea and afterward consolidated. The colors are dull gray, 

 bluish, brownish, to black. The composition is usually the same as 

 that of calcite, carbonate of lime (p. 55), except that impurities, as 

 clay or sand, are often present. In texture, they vary from an earthy- 

 looking limestone to a very compact semi-crystalline one ; and from 

 this kind the passage is gradual also to the true crystalline. 



(2.) Magnesian Limestone or Dolomyte (page 55). — Consists 

 of carbonate of lime and magnesia, but is not distinguishable in color 

 or texture from ordinary limestone. The amount of carbonate of 

 magnesia present varies from a few per cent, to that in dolomite. 

 Much of the common limestone of the United States is magnesian. 

 That of St. Croix, Wisconsin, the "Lower Magnesian," afforded 

 Owen 42-43 per cent, of carbonate of magnesia, 48-24 carbonate of 

 lime, with 8-84 of sand, oxyd of iron and alumina, and 0*40 moisture. 



In some limestones the fossils are magnesian, while the rock is common limestone. 

 Thus, an Orthoceras in the Trenton limestone of Bytown, Canada (which is not mag- 

 nesian), afforded T. S. Hunt — Carbonate of lime 56-00, carbonate of magnesia 37-80, 



