now deposited on the earth's surface, is deposited from waters that are raised to an intense heat, and instead of uniting to form sand or gravel, takes the shape of incrustations on stems, leaves, and other objects on which it happens to be thrown down. As absolute proof as the lapse of many ages, without a solitary addition to their countless throng, can form, exists therefore, that neither the chemical agents are now in activity, nor the waters of the ocean in the conditions that are requisite to their production. The fancy that they are, is as palpably against the fact, and as irreconcilable with the laws that now govern the modifications of matter, as it were to imagine that new suns are forming in our firmament, or new moons generating to revolve with ours around our earth. Such is the fact, also, with lime. No deposits of that mineral now take place on the surface, except such as is thrown up by springs, and is derived therefore from the strata over which those waters run and that, on its deposition, forms a loose porous mass, essentially unlike the limestones from which it is drawn. Not a grain is added by the process to the general mass of the mineral. There is only a transference of particles from earlier formations that lie at a considerable depth, and union of them again at the surface in a new form. But if the causes that originally gave birth to the vast beds of limestone that occur throughout the whole series, from the earliest

to the latest of the stratified rocks, are still in uninterrupted activity, and generating new deposits on as great a scale as at former periods, why is it that none of these new formations are noticed or discovered? Why is it that not a particle can be shown to be added to the aggregate? What can be more unscientific than thus to maintain the continued activity and undiminished energy of causes that once operated on so immense a scale and generated such massive products, though no fruits whatever are seen of their present agency; though the most indisputable proofs of their discontinuance for ages are presented in the fact, that through that long period they have not given birth to any of their proper effects?

Chalk was, in like manner, the product of peculiar causes acting in peculiar circumstances for a limited. period. It is not, like limestone, sandstone, and shales, distributed in frequent beds throughout the whole series of the strata, but occurs only in a single group near the close of the secondary formation. Nor is it generally diffused like many of the earlier and later deposits, or found in all the localities where the other members of the group to which it belongs occur. Instead, it is confined to comparatively narrow limits.

'Respecting the geographical distribution of the cretaceous group. . . . throughout the British Islands, a large part of France, many parts of Germany, in Poland, Swe

den, and in various parts of Russia, there would appear to have been certain causes in operation, at a given period, which produced nearly, or very nearly the same effects. The variation in the lower portion of the deposit seems merely to consist in the absence or presence of a greater or less abundance of clays or sands, substances which we may consider as produced by the destruction of previously existing land, and as deposited from waters which held such detritus in mechanical solution. The unequal deposit of the two kinds of matter in different situations would be in accordance with such a supposition. But when we turn to the higher part of the group, into which the lower portion graduates, the theory of mere transport appears opposed to the phenomena observed, which seem rather to have been produced by deposit from chemical solution of carbonate of lime and silex."Sir H. T. De La Beche's Manual, p. 259.

The limitation of this formation to a single period and to a narrow area, is thus wholly irreconcilable with the theory that geological causes act at all periods and with a uniform energy. If that postulate were true, chalk should exist, and on as great a scale in the different groups of the primary and earlier classes of the secondary formations, as it does in the series to which it gives its chief characteristic. It should occupy a proportional place also among the tertiary strata, and be in the process of formation at the present time. No indications appear, however, of such formations since the commencement of the tertiary

period. Can a more decisive proof be demanded of the error of that postulate? Can a proposition be advanced in more direct and palpable repugnance to facts?

Rock salt, in like manner, instead of being interspersed like sandstone, limestone, and shale, through the whole succession of the strata, as the theory of the uniform activity and energy of geological causes requires, is mainly confined to a single era. There are examples, indeed, of the rise of salt springs, as in this State, from the New York or Silurian system. Even they, however, are generally associated with the new red sandstone, or the groups with which that is immediately connected; and rock salt itself occurs chiefly in that formation. Though found in every quarter of the globe, it is not, like sandstone and shale, a universal deposit, but exists only in patches, or districts widely separated from each other. It is in some localities several hundred feet in thickness. Geologists, however, instead of being able to point out any exemplification in the processes that are now going forward of the mode in which it was formed, have not hitherto succeeded in presenting any probable theory of its origin.

"It is not surprising that the origin of rock-salt has been a subject of much inquiry among geologists; yet nothing like a rational theory has yet been offered. It is far easier

to show that the most simple and obvious hypothesis is wrong or imperfect than to propose a probable one. The origin of gypsum is not less mysterious, even with every conjecture we can make respecting the presence and acidification of sulphur; yet this inquiry has never excited the same anxiety. No rational explanation has yet been suggested; and I have none to offer. But we must seek for the greater ambition of geologists on the subject of salt, in their wish to derive these deposits from the waters of the ocean in a simple and direct manner; seizing on one obvious analogy only, to the neglect of other possible modes of explanation. That it has been the produce of the ocean is possible, since the rocks among which it is found are indebted for their existence to the same source. Yet no obvious method of accounting for its peculiar appearances or limitation can be engrafted on that general admission; while it were as well for geology, and in other matters than this, if they who deposit pure rock salt in the Mediterranean at this day, would learn at least as much of chemistry as the 'Chemist' of three blue bottles. The desiccation of saline lakes will not account for it, because subterranean salt is far more pure than that which must be the produce of the evaporation of the sea. The mode in which it is disposed will not admit of this explanation; and still less can any system of evaporation account for the concretionary structure of the salt of Cheshire.

"To these difficulties it must be added that the depth of sea-water required to produce in this manner some of the larger masses known in Europe, is incomprehensible. It