The grand generalizations of Lyell have been strengthened since his death by more complete investigations of certain phenomena and their causes than were possible in his day; while the only objections to them seem to be founded, to some extent, upon a misconception. He has been termed a “Uniformitarian,” and it is alleged that it is unphilosophical to take the limited range of causes we now see in action, as a measure of those which have acted during all past geological time. But neither Lyell nor his followers make any such assumption. They merely say, we do not find any proof of greater or more violent causes in action in past times, and we do find many indications that the great natural forces then in action—seas and rivers, sun and cloud, rain and hail, frost and snow, as well as the very texture and constituents of the older rocks, and the mode in which the organisms of each age are preserved in them, must have been in their general nature and magnitude very much as they are now. Other objections, such as that the internal forces were greater when the earth was hotter, and that tidal effects must have been more powerful when the moon was nearer the earth, are altogether beside the question until we can obtain more definite measures of past time than we now possess in reference to both geological and cosmical phenomena. It may well be that the physical changes above referred to have been so slow that they would have produced no perceptibly increased effect at the epoch of the early stratified rocks. Lyell’s doctrine is simply that of real against imaginary causes, and he only denies catastrophes and more violent agencies in early times, because there is no clear evidence of their actual existence, and also because known causes are quite competent to explain all geological phenomena. It must be remembered, too, that uniformitarians have never limited the natural forces of past geological periods to the precise limits of which we have had experience during the historical period. What they maintain is, that forces of the same _nature_ and of the same _order of magnitude_ are adequate to have brought about the evolution of the crust of the earth as we now find it. ORGANIC EVOLUTION, ITS LAWS AND CAUSES We now come to that branch of the subject which is the most important and distinctive of our age, and which, in popular estimation, alone constitutes evolution—the mode of origin of the innumerable species of animal and plant life which now exist or have ever existed upon the earth.