irresistible, it amounts to demonstration, that the ocean covered the spot where the shell was found, and remained there during a long period of time, for the limestone is formed almost entirely of shelly fragments; and that vegetation with all its conditions, light and heat, soil and atmosphere, once existed where the fragile plant was preserved. It could not have been transported thither, for its delicate texture would have been injured in the removal, whereas its fibres are as nicely preserved as if the plant had been carefully enclosed between the leaves of a book.

Not only are some of the facts opposed to all experience and previously-acquired ideas, as we have seen, but Geology also involves an apparent contradiction of terms-for the lowest in the series sometimes occupy the highest level, and vice versa. Thus on the continent of Europe, the lowest bed, the primitive granite, on which all the other rocky masses repose, rarely makes its appearance except on the summits of the highest mountains, such as Mont Blanc and the Jung Frau, and the loftier Alps, which

"Pinnacle in clouds"

"Their snowy scalps"

presenting in these cases, not horizontal beds, as their position at the base of the whole superstructure of stratified rocks might lead us to infer, but sometimes cones of vertical strata of inconceivable height, which tower in majestic grandeur far above the reach of human footsteps,

"As if to shew"

"How earth may rise to heaven, yet leave vain man below."

Such are some of the anomalies to be encountered in the study of Geology.

It is the uniformity of superposition, the invariable order of succession, sometimes disturbed but never inverted, on which Geology depends as a practical science: the identity of a rock being proved by the fossils it contains, its position in the series is at once ascertained, and by a never-failing analogy, the position of other rocks is accurately inferred. It is a knowledge of these facts which guides the skilful miner in his expensive operations, and it is in defiance or ignorance of them, that the many abortive searches for coal have been conceived and prosecuted at so great a sacrifice of the national wealth. The often-cited case of Bexhill, near London, in which eighty thousands pounds are said to have been expended in a fruitless search for coal, which the merest tyro in Geology would in the present day have condemned, is of itself sufficient to prove the immense advantage of Geology as a practical science.

It is unnecessary to dilate upon the inestimable advantages, we derive from the skill of the miner. It would be no difficult task to prove that our mineral resources are the main-spring of our national prosperity, and one of the chief causes of that proud pre-eminence which this country occupies in the scale of nations ;-supplying us on the one hand with coal, the vital principle of manufactures, on the other with iron, the raw material of the most considerable portion of our national industry-the basis of so much ingenuity, the source of incalculable wealth and how great is the aid which the science of Geology has afforded to the miner:-how it has systematized his operations-how it has extended and is daily enlarging his dominion, they only who are practically

C

interested in the subject, and have watched the progress of the art of mining, can form an adequate estimate.

A most gratifying instance of the successful result of an enterprize, based upon geological deductions, has lately occurred in the north of England, at the Monkwearmouth colliery. The works in this case were commenced on the line of the Magnesian limestone, which, as all who are acquainted with the outlines of English Geology are aware, overlies on its eastern edge, the great northern coal-formation, throughout its whole extent from the Trent to the Tyne. The coal had never been worked * in this situation, and there was nothing on the surface to indicate its existence beneath, as there usually is in coalfields: but assured of its presence by the well-known fact that the general dip, or downward inclination of the strata was in this direction, the spirited proprietors, (Messrs. Pemberton and Thompson,) relying upon the infallible order of succession which I have just described, resolved, whatever might be the cost, to reach it. At the depth of three hundred and fifty feet they first found traces of the existence of coal, but many hundred feet of strata were subsequently passed through, and no workable seam of coal discovered. Still convinced, however, of the accuracy of the conclusions which had led them to embark in the undertaking, guided in fact by the light of science, they pursued their object with undaunted perseverance, and at the depth of one thousand six hundred feet from the surface, or one thousand five hundred and thirteen feet below the level of the adjacent ocean, a depth far greater than had ever before been

* Getting the coals is termed by miners working them.

reached in sinking for coal,* after many years of toil and anxiety, and the outlay of an enormous sum of money, they met with the reward of their efforts in a valuable bed of coal! The identity of this bed being proved, the

* The following statement of the comparative depth of some of the principal mines in the world, and of the magnitude of mining operations, may not be uninteresting:

DEPTH OF MINES.

Kits pühl Copper mine, in the Tyrol mountains
Sampson mine, at Andreasberg, in the Harz

The deep mines in the Tyrol, the Harz, and the Andes, above described, are all in high situations; the bottom of the Mexican mine, for instance, is 6000 feet higher than the top of the Cornwall shafts. The deepest perforation beneath the level of the sea, consequently the nearest approach to the earth's centre, has been made at the Monkwearmouth Colliery, above described. Pearce's shaft, Cornwall, (1338 feet below the level of the sea), was until lately, the deepest in the world; the superiority of depth however must now be ceded to Monkwearmouth, which is 1513 feet below the surface of the German Ocean.

The Consolidated mines in Cornwall, have 95 shafts, or vertical pits, 25 miles in length. There are also four steam engines, with cylinders 90 inches in diameter; and it is calculated that if horse-power were used, as formerly, to drain the mines, 55,000 horses would be required for this purpose in Cornwall alone.

The Valenciano mine, in Mexico (1770 feet deep), has a vertical shaft of an octagonal form, 30 feet in diameter, walled throughout with beautiful masonry, the cost of the construction of which, was £220,000! The annual produce of the mine is £600,000, and 3000 persons are constantly employed.

existence of others beneath is inferred with so much confidence, that the works will be continued until the "Hutton" or most valuable seam in that district is reached. * This instance will illustrate the importance of the determinate order of succession which Geology has disclosed. Thus, the beautiful surface of this favoured island, here raised into hills, there furrowed into valleys-here broken into craggy steeps, there expanding into fertile plains, which presents to the inexperienced eye an heterogeneous mass of earthy matter confusedly mixed together, the geologist discovers to be composed of a series of distinct and well-defined mineral masses, each possessing, not only a peculiar character, but a certain geographical distribution; so that had the conductors of the project above described, made a similar perforation in the strata of the eastern or southern part of the island, disappointment instead of success would have been the result of their exertions; in fact, they might in such situations, have bored through the earth's centre to the antipodes, before they met with the object of their search.

It is a singular fact, and one highly favourable to the study of Geology in this country, that our island presents us with an epitome, if it may be so termed, of the greater part of the regular solid strata which compose the crust of the globe-a model in miniature, nicely arranged and accurately defined, of the rocky

* The northern coal-field, from which London draws its immense supplies of fuel, is known to be rapidly approaching to exhaustion. The success of this experiment will in all probability add several centuries to the lease by which it has so long held the London market.