VARYING CONDITIONS OF STRATIFICATION.

57

thus elevated, and left with an irregular outline, LECT. II. the waters in flowing off carried down the loosened materials, and, in different extent and degree, left bare the stony masses.

XI. But it is upon reflection obvious, and the Subsidence. geological evidences of the fact are numerous and decisive, that the ebullient action of the firemelted liquid below is likely to produce undulations of the surface, and therefore, in some places, to cause diminutions of density, and perhaps vast caverns filled with aëriform fluids. The crust of the earth, over these less solid spots, will be weakened, and a sinking down will take place through, it may most probably be, a large area of the surface. These subsidences may, in some rare cases, be rapid: but generally they, as the elevations, will be extremely slow.

and compli

stratifying

XII. Now I fear that I must put to trial the Differences patience of my friends in an attempt to describe cation of in words a complicated series of operations, processes. which, by arguing from effect to cause, we have sufficient reason to believe must often have taken place, in ways equivalent to what I request you to conceive. But this is not the forming of an imaginative hypothesis: it is no more than expressing in the form of simple narrative, facts of whose separate reality we have the fullest evidence, and the consecutive occurrence of which we consider as in the highest degree probable.

Let the mind represent to itself a large space of the bed of an ancient ocean, into which the

58

VARYING CONDITIONS OF STRATIFICATION.

LECT. II. sedimentary materials from the land have been transported, through a period of time to us immeasurable. Along this extended surface the deposits, in the varieties which changing circumstances in both the land and the waters have produced, are spread. By the weight of an ocean five or six miles in depth, and by the antagonist pressure, with more or less intensity, of heat from the underlying fires, this formation is consolidated. A series of movements from below raises up a portion of this deposit; till it is above the water-level, with its hills and dales and susceptibilities of further variation of surface. Ages roll on. Other strata are laid upon the portion of the area which had not partaken of the elevating movements; or which may have moved in the contrary direction; that is, may have sunk down so that a difference of mineralogical (called also lithological) character is produced over it. The former portion long lies as a part of the dry land, is washed over by rains and rivers, and is subjected to other causes of superficial change; then it becomes subject to the process of slow subsidence, consequent upon some great change in the fiery region below, and it becomes once more the bed of oceanic waters. Here, in due but various process of time, it is overspread with a new stratum, differing from its own preceding surface, and from the one or several strata which had in succession been laid upon the portion not elevated during

REPETITIONS.

59

the whole period; the difference being probably LECT. II. in mineral composition and texture, but more certainly in the character of vegetable or animal remains which are imbedded in it. Now the new body of deposits may be identical over the entire extent first supposed. It is manifest, therefore, that in one part the last stratum will rest upon the foregoing one, which had been long elevated and exposed to causes of change; and thus the surfaces at the junction will be irregular: but, upon the portion which had not been raised out of the waters, or which had sunk, one stratum or several have been deposited throughout the intervening period, and they will probably rest conformably, each upon that below it, that is, their bounding surfaces will correspond to each other in lines nearly parallel. The whole area comes afterwards to be elevated; or only some parts of it. One part, therefore, possesses a series of strata which are not found in the other; and that other, if studied alone, might suggest the idea that two formations naturally came together, or that the upper always followed the lower at once, while yet between them in reality some others have intervened.

These operations of deposition, elevation, subsidence, and elevation again, in application to separate districts, and in different periods through an indefinite duration,-have been repeated a number of times; each repetition producing breaks, fissures, and manifold displacings, erec

LECT. II. tions, and inclinations, of the more hard and consequently frangible strata; and bendings, even to a complete overturning, or contortion backwards of the softer and more coherent ones. The evidence of elevation and that of subsidence occur frequently within moderate geographical limits; so that two districts with their intervening ground may be familiarly compared to a long board, balanced on a fulcrum: when one end sinks the other rises.

Triumph of investigation

tion.

The miscellaneous result might seem to baffle and induc- all attempts at arrangement and safe induction : but the labours of distinguished men, most of them our admirable contemporaries, in the field of actual investigation, with astonishing toil and perseverance, guided by cautious judgment and habits formed in the study of the exact sciences, have triumphed over what might have appeared a hopeless confusion; and have reduced to a certainty scarcely short of sensible and mathematical proof, the modes of deposition, the order of original succession, and in many cases that of subsequent change.

The order of succession never violated.

From the description which I have endeavoured to give, it will be easily understood, that the order of succession is never transgressed; though particular formations, one, two, or more, in a system or subdivisional group, and of course many in the whole series, may and must be wanting. Those formations either have never existed, from the course of operations which I

REMAINS OF ONCE LIVING CREATURES.

61

have attempted to describe; or they have been LECT. II. removed by the nearly horizontal action of

water, washing away large masses of strata, scattering and diffusing their materials upon the floor of the ocean, and thus producing new formations.

and new

XIII. To such removals, occasion has been Denudations given by the elevations and depressions so fre- depositions. quently before mentioned. These have exposed the softer or previously loosened materials, to the incursion of mighty bodies of water, which have washed them away, carried them out to shorter or longer distances, dropping the coarser and heavier portions the earliest, holding longer in muddy mixture and transporting to the greater distances the fine and light particles, spreading them out under the great seas; and there these new strata have been disposed variously, according to circumstances arising from the form and constitution of the bottom, the direction of currents, volcanic action below the bed of the sea, molecular aggregation of similar substances, and chemical attractions. This kind of change, in relation to the area from which the surface has been swept off, is called Denudation.

ment of

mains.

XIV. While these mineral formations were commencethus in progress, their masses yet soft were re- organic replenished with the remains of animals which had lived in the waters; skeletons, coverings, shelly habitations, and even soft parts some of which still exhibit their vestiges. In all the formations,