Geology of England and Wales. 151 
2. Millstone grit and shale. 3. Carboniferous, or mountain 
limestone. 4. Old red sandstone: and in forming an accurate 
notion of the geology of our coal districts, we shall be much 
assisted by keeping in view the mutual relations and connexions 
of these four substances ; remembering, always, that although 
carbonaceous beds occur in other formations, it is only in the 
limits of the strata at which we have now arrived, that supplies 
of coal capable of being profitably worked are to be found. 
The coal strata, or coal measures, as they are often called, 
“ consist of a series of alternating beds of coal, slate-clay, and 
sandstone, the alternations being frequently and indefinitely re- 
peated.” The slate-clay or shale differs from clay slate by its 
want of solidity and induration; the sandstones are usually 
gritty, micaceous and tender; they are used for building, 
paving, and the manufacture of grindstones. These strata also 
afford nodules of clay ironstone, the ore, whence the principal 
supplies of that important metal are derived in this kingdom. 
“The occurrence,” say our authors, “ of this most useful of 
metals, in immediate connexion with the fuel requisite for its 
reduction, and the limestone which facilitates that reduction, is 
an instance of arrangement so happily suited to the purposes of 
human industry, that it can hardly be considered as recurring 
unnecessarily to final causes, if we conceive that this distribution 
of the rude materials of the earth, was determined with a view 
to the convenience of its inhabitants.” 
The organic remains of the coal strata are abundant and 
curious, especially those of the vegetable kingdom; they con- 
sist in the trunks, leaves, and seed vessels of various plants, all 
distinct from species now existing, but agreeing with the pro- 
ducts of hot climates, and of moist situations ; arundinaceous 
plants and ferns are very plentiful. The few shells that have 
been discovered are apparently marine, not fluvial. 
The inclination of these strata is one of the most remarkable 
points in their geological history ; they are generally inclined, 
and often ata very high angle, being quite unconformable to the 
more horizontal overlying beds; they also exhibit other irregu- 
larities, among which the great fissures which traverse them, 
often extending for several miles, deserve peculiar notice. These 
faults as they are provincially called, sometimes occasion a 
change of level exceeding 500 feet, one of the walls being ele- 
vated, or the other depressed to that amount, showing the 
agency of some violent convulsion which has thus divided the 
strata, and occasioned a tremendous vertical dislocation. 
The coal measures rest upon beds of shale and of millstone 
grit, which is a coarse grained sandstone, more indurated than 
that which subdivides the strata of coal; it contains occasional 
beds of bituminous limestone, thin seams of an indifferent coal, 
nodules of ironstone, and abundance of pyrites, and is occa- 
