I placed before you in a few words, some little time ago, a statement of the sum and substance of Milton’s hypothesis.  Let me now try to state as briefly, the effect of the circumstantial evidence bearing upon the past history of the earth which is furnished, without the possibility of mistake, with no chance of error as to its chief features, by the stratified rocks.  What we find is, that the great series of formations represents a period of time of which our human chronologies hardly afford us a unit of measure.  I will not pretend to say how we ought to estimate this time, in millions or in billions of years.  For my purpose, the determination of its absolute duration is wholly unessential.  But that the time was enormous there can be no question.

It results from the simplest methods of interpretation, that leaving out of view certain patches of metamorphosed rocks, and certain volcanic products, all that is now dry land has once been at the bottom of the waters.  It is perfectly certain that, at a comparatively recent period of the world’s history—­the Cretaceous epoch—­none of the great physical features which at present mark the surface of the globe existed.  It is certain that the Rocky Mountains were not.  It is certain that the Himalaya Mountains were not.  It is certain that the Alps and the Pyrenees had no existence.  The evidence is of the plainest possible character, and is simply this:—­We find raised up on the flanks of these mountains, elevated by the forces of upheaval which have given rise to them, masses of Cretaceous rock which formed the bottom of the sea before those mountains existed.  It is therefore clear that the elevatory forces which gave rise to the mountains operated subsequently to the Cretaceous epoch; and that the mountains themselves are largely made up of the materials deposited in the sea which once occupied their place.  As we go back in time, we meet with constant alternations of sea and land, of estuary and open ocean; and, in correspondence with these alternations, we observe the changes in the fauna and flora to which I have referred.

But the inspection of these changes give us no right to believe that there has been any discontinuity in natural processes.  There is no trace of general cataclysms, of universal deluges, or sudden destructions of a whole fauna or flora.  The appearances which were formerly interpreted in that way have all been shown to be delusive, as our knowledge has increased and as the blanks which formerly appeared to exist between the different formations have been filled up.  That there is no absolute break between formation and formation, that there has been no sudden disappearance of all the forms of life and replacement of them by others, but that changes have gone on slowly and gradually, that one type has died out and another has taken its place, and that thus, by insensible degrees, one fauna has been replaced by another, are conclusions strengthened by constantly increasing evidence.  So that within the whole of the immense period indicated by the fossiliferous stratified rocks, there is assuredly not the slightest proof of any break in the uniformity of Nature’s operations, no indication that events have followed other than a clear and orderly sequence.