30. And in the meanwhile, to complete the view thus taken by the uniformitarian of the geological history of the earth, by some constant but inscrutable law, creative agency is perpetually at work, to introduce, into this progressive system of things, new species of vegetable and animal life. Organic forms, ever and ever new ones, are brought into being, and left, visible footsteps, as it were, of the progress which Time has made;--marks placed between the rocky leaves of the book of creation; by which man, when his time comes, may turn back and read the past history of his habitation. But the point for us to remark is, the immeasurable, the inconceivable length of time, if any length of time could be inconceivable, which is required of our thoughts, by this new assumption of the constant production of new species, as a law of creation. We might feel ourselves well nigh overwhelmed, when, by looking at processes which we see producing only a few feet of height or breadth or depth during the life of man, we are called upon to imagine the construction of Alps and Andes,--when we have to imagine a world made a few inches in a century. But there, at least, we had _something_ to start from: the element of change was small, but there _was_ an element of change: we had to expand, but we had not to originate. But in conceiving that all the myriads of successive species, which we find in the earth's strata, have come into being by a law which is now operating, we have _nothing_ to start from. We have seen, and know of, no such change; all sober and skilful naturalists reject it, as a fact not belonging to our time. We have here to build a theory without materials;--to sum a series of which every term, so far as we know, is nothing;--to introduce into our scientific reasonings an assumption contrary to all scientific knowledge. 31. This appears to me to be the real character of the assumption of the constant creation of new species. But, as I have said, it is not my business here, to pronounce upon the value or truth of this assumption. The only use which I wish to make of it is this:--If any persons, who have adopted the geological view which I have just been explaining, should feel any interest in the speculations here offered to their notice, they must needs be (as I have no doubt they will be) even more willing than other geologists, to grant to our argument a scale of time for geological succession, corresponding in magnitude to the scale of distances which astronomy teaches us, as those which measure the relation of the universe to the earth. This being supposed to be granted, I am prepared to proceed with my argument. CHAPTER VI. THE ARGUMENT FROM GEOLOGY.