CARBONIFEROUS LIMESTONE. 89 



but occasionally granular or lameilar. It contains 

 imbedded crystals of calc spar, and sometimes pass- 

 es into magnesian and argillaceous carbonates of 

 lime. It not only alternates with the lower beds 

 of the coal measures, but also with the upper beds 

 of the surrounding group. It appears in caverns of 

 great extent both in Europe and this country. 



j This limestone is of various colours, from white, 

 passing through all the shades of gray, to black. It 

 is often coloured and variegated by metallic oxides, 

 yielding some of the most beautiful marbles. In- 

 England it forms high mountains, and is therefore 

 called mountain limestone. In this country it oc- 

 cupies a vast extent, extending from Michilimack- 

 inac on the north, to Kentucky and still farther 

 south. The lead-mines of Illinois and Missouri are 

 contained in it. It should be noticed that the coal 

 of this formation may be of every quality, from an 

 anthracite containing little or no hydrogen, to that 

 which is richest in bitumen. The same stratum 

 often contains both anthracite and bituminous coal, 

 the former where it lies near the surface of the 

 earth, or is traversed by dikes of trap. As this 

 was thrown up in the form of lava or in a heated 

 state, we thus account for the fact that the coal in 

 the vicinity of trap-rocks contains no bitumen, the 

 volatile matter having been thrown off by the heat. 



In order to place before the reader an actual 

 view of the formations in which coal has been 

 found, we shall now present sections of some of 

 them in Europe, which may serve as a kind of 

 guide to explorations in search of this mineral. 



GENERAL ARRANGEMENT OF THE CARBONIFEROUS 

 SYSTEM. 



1. The Coal Measures. 

 (Beginning at the surfV* 



1. Sandstone. 



2. Shale or sUte. 



' . li 



