The collieries of Great Britain are now upon the most extensive scale, and are of the first importance to the kingdom ; both as regarding its political and commer cial interests ; so much so, that it is evident, without cheap coal, the manufactories of Great Britain could not be brought forward in competition with those of the other nations of the world, where manual labour is com paratively very low ; in short, the coal-mines of Great Britain loim a physical and prominent point in the poli tical state of the empire. The capitals employed in the collieries, and in the shipping connected with them, are immense, amounting to many millions. A very consi derable proportion of the population of the kingdom is employed in the mines and coal trade, while the ships which carry coals coastwise, are a nursery for thousands of the most intrepid seamen which are to be found in the world.
It cannot easily be estimated what is the total pro duce of coals in Britain, but it must extend to many millions of tons ; for it is known that the output of coal upon the rivers Tyne and Wear, in the counties of Northumberland and Dui ham, amounts to three millions of tons annually, of which only a small quantity is used in the district, the greater part being shipped coastwise. In these two districts alone, it is estimated that 70.000 people are employed in the coal trade, and that the capi tal invested in the collieries and shipping is above two millions and a half of money.
With regard to the formation of coal, many theories have been brought forward ; but although these display no common share of genius and patient investigation, they have hitherto led to nothi.tg conclusive ur tory on the subject. The object in this treatise is. to give a distinct view of the geological situation of coal fields, their absolute forms, the dislocations and troubles which occur in them, and the method of working coal mines.
The great coal-field of Britain, which is composed of numerous subordinate coal-fields, crosses the island in a diagonal direction, the south boundary line extending from near the mouth of the river Humber, upon the east coast of England, to the south part of the Bristol channel on the west c oast ; and the north boundary line extending from the south side of the river Tay in Scot land, westward, by the south side of the Ochil mountains, to near Duritharton, upon the river Clyde; within these boundary lines North and South Wales are included. This area is about 260 miles in length, and, on an ave rage, about 150 miles in breadth. Within these bounds all the chief coal-fields are found upon which collieries have been established in Britain ; and no coal-field of any consequence has been found, either to the north or south of the lines above mentioned, excepting some small patches of thin coals of inferior quality, and the coal field of Brora in Suthcrlandshire, Scotland, which is far disjoined from any other coal-field.
When we take a cursory view of this globe of earth, composed of high, wild, and rocky mountains, its nume rous valleys, rivers, and undulated surface, together with the vast expanse of ocean, we are apt to consider the mountains and rocks as forming a kind of chaos, without regularity or order ; but the laborious and patient inves tigations of mineralogists have shown, that there is in the arrangement of the various rocks, an order and regu larity beyond what was, or is, commonly imagined,—a regularity, perfectly consistent with that Infinite wisdom and Almighty power which formed the vast, the un bounded system of the universe. It is this regularity in the succession and arrangement of the various rocks, from the Alpine heights to the valleys and level of the sea, which guides the mineralogist in his investigations, when searching for those minerals which are so benefi cial to man in his state of civilized society.
Mineralogists have divided the rocks which compose the globe into four classes, viz.
I. Primitive Rocks.
2. Secondary, or Transition Rocks.
S. Floetz, or Newer Secondary Rocks. 4. Newest Floetz Trap Rocks.
In the primitive class of rocks, granite, which gene rally forms the highest parts of mountain ranges, is reck oned by mineralogists to be the lowest series of rocks, and upon which all the other rocks rest.
It is worthy of particular remark, that the four classes of rocks before mentioned, lie in regular succession, the primitive rocks being the lower series, and the newest floetz trap rocks being the last in succession ; and although the rocks composing each of the four classes may alternate variously with each other, yet the order of the four classes has never been found inverted ; that is, the primitive and secondary rocks have never been found overlaying the other two classes of what are termed newer floetz rocks.
Beds of coal have not hitherto been found in the pri mitive or transition class of rocks, but they are found in great abundance in the third class, termed the floetz cr newer secondary rocks. Coals are also found in the newest floetz trap formation ; but the coal-fields are not extensive, though they are sometimes of uncommon thickness.