interesting results of geological enquiry; and we may here witness all the effects of volcanic phenomena without their attendant danger and inconvenience. They belong, however, to a period antecedent to what we have regarded as contemporary times, the events of which we are considering.

An active agent of change in the structure of the earth's surface, constantly but quietly at work, is found in the organic creation. Rock-formations of vast extent, are in progress in many parts of the ocean, effected by the labours of the well-known coral animals, or animal plants * as they are termed, from the circumstance of their branch-like habitations, always being found springing from rocks. These polyparia, in com mon with the other shelly inhabitants of the ocean have the extraordinary property of secreting (from whence derived is not known) an enormous quantity of carbonate of lime in the construction of their dwellings. Affixing themselves to the submarine mountains or elevated portions of the bed of the ocean, they spread their myriad arms, and rapidly build up the ramified substance, which is in this country admired for its beautiful forms. In their progress upwards one generation builds upon the ruined and deserted habitations of another, calcareous sand and other cementing matter furnished by the ocean, is mixed with the mass, and the whole becomes a consolidated limestone; which, as it emerges from the water, decomposes and becomes eventually the abode of vegetation, birds make it their resort, animals accidentally transported by the waves find in it a refuge

* Zoophytes.

from a watery grave, and man at last finds his way thither, erects his habitation, cultivates the decomposing soil, now enriched with nutritive matter and adorned with vegetable productions, and calls himself "lord" of this new creation. This creative process is going on to an incredible extent in various parts of the world. Reefs, as these newly-built islands are called, extending many hundred miles, are forming in the tropical regions of the Pacific. The Indian ocean teems with this world-building population, and its insidious encroachments are fast filling up the Arabian gulph.

Springs, although upon a small scale, are actively engaged in adding to the mineral masses in the earth's superstructure. All waters issuing from beneath the surface of the ground, contain more or less of earthy matter in solution, and it is to these extraneous ingredients that the "crystal spring" owes its clearness and agreeable taste. Lime is the predominating substance in mineral waters, in which it is held in solution by means of carbonic acid-and where this element is abundant as in the case of thermal, or hot springs, the water is sometimes saturated with the carbonate. The carbonic acid being, in these cases, withdrawn by the abstraction of heat, and other circumstances, a large deposit of limestone takes place, as in the Solfatara, and on the banks of the Anio, at Tivoli, and in many other situations in the neighbourhood of Rome: the principal buildings in "the eternal city," in fact, are built of this rock of modern origin. The rapidity with which this concretionary deposit is effected is not less incredible than the great extent of its formation. I have seen specimens of travertin or tufa, as it is termed, equal in

hardness and beauty of crystallization to the hardest marble, which had formed in considerable masses in the short space of twelve months. Sir Humphry Davy mentions in his "Consolations of Travel" that he fixed a stick on a mass of travertin, in the lake of the Solfatara, covered by the water in May, and in the April following, he had some difficulty in breaking, with a sharppointed hammer, the mass which adhered to the stick, and which was several inches in thickness. At San Fillippo, in the same neighbourhood, water, charged with lime and magnesia, has been known to deposit a solid mass of rock thirty feet thick, in twenty years: and in other localities where this deposition is going on, it has formed hills or monticules a hundred and fifty feet high, or filled up valleys of equal depth.

But the changes effected in the configuration of the earth's exterior by the operation of this, and all the agents we have hitherto considered, are unimportant and inconsiderable-the sport of pigmies compared with the labours of Titans-when contrasted with the effect of the same causes, operating under different circumstances, at remote periods in the history of the globe. Even within the historical period since the earth assumed its present outline, and subsequently to the period when man first became its denizen, this "goodly fabric" has been threatened with destruction and overwhelmed by great physical catastrophes. It is in the investigation of the relics of these events, that geology in the popular acceptation of the term may be said to commence. Contemporaneous causes are entitled to consideration, not so much on account of their magnitude, as in con

sequence of the theory which has been built upon an exaggerated view of their effects.

The earliest and clearest evidence of the great physical convulsions which the globe has experienced, is found in the fragments of rocks, erratic blocks as they are termed, organic remains, and gravel, scattered in such profusion over the surface of all our continents and islands. By an examination of the nature and mineral character of these, we not only discover the source from whence they have been derived, but can form an idea of the force by which they were rent from their original position and

"Hurl'd with restless violence round about The pendent earth."

These travelled fragments are generally supposed to be the relics of the last general catastrophe-the ruins of the world antecedent to the one we now occupy; for we shall find as we proceed that the earth and "all that it inhabit," have undergone strange mutations-that new worlds, in fact, have repeatedly been raised upon the wreck of old-and the habitable surface again and again destroyed and renewed.

The most familiar of these diluvial phenomena, are the gravel beds dispersed through the valleys, and sometimes occupying the hills, in this and every other country. They generally consist of an accumulation of fragments, rounded by attrition in the act of rolling, and organic remains, from the neighbouring rocks. Some of the most prominent hills of the island appear to have furnished these materials in the greatest abundance: thus Dr. Buckland has traced fragments of the

Lickey Hill, a remarkable mass of quartzose sandstone, near Birmingham, in all the valleys diverging southwardly from that part of England, and has shewn in his "Reliquæ Diluvianæ," that they were drifted to a great distance along the valleys of the Evenlode, the Cherwell, and the Thames, through two remarkable openings in the range of limestone hills near Banbury, and at Moreton-in-the-Marsh, the only points where this effectual obstac to their dispersion in that direction, appears to have given way to the denuding torrent.

The citizen of London, whose travels had never extended beyond the district of the two-penny post, and the range of whose ideas was, perhaps, confined within still narrower limits, would hear with surprise and incredulity, that the pebbles which he sees dug from beneath the soil of Hyde Park, had travelled from the neighbourhood of Birmingham. Yet this is as easily proved, as that Westminster bridge is built of Portland stone, and the new London bridge of granite.

A vast accumulation of gravel covers the eastern side of Leicestershire, and runs through the adjoining county of Northampton, from which, according to the statement of Conybeare, a complete suite of geological specimens might be obtained. Thus, in the deep gravel of Leicestershire, I have found specimens of the echinus and the encrinite, buried in the same bed, although they belong to widely-different ages, and were originally deposited in localities far removed from each other. These gravel beds contain also, washings from the neighbouring coal-formation, which in many cases, as at Billesdon, from their peculiar specific gravity,