CARBONIFEROUS LIMESTONE. 89 
but occasionally granular or lamellar. 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. 
This limestone is of various colours, from white, 
passing through all the shades of gray, to black. It 
is often coloured and variegated by metalUc 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 surfs<»» 
1. Sandstone. 
2. Shale or »Ute. 
H2 
