It will, I trust, be found, that in dealing with errors which, in at least their primary bearing, affect questions of science, I have not offended against the courtesies of scientific controversy. True, they are errors which also involve moral consequences. There is a species of superstition which inclines men to take on trust whatever assumes the name of science; and which seems to be a reaction on the old superstition, that had faith in witches, but none in Sir Isaac Newton, and believed in ghosts, but failed to credit the Gregorian calendar. And, owing mainly to the wide diffusion of this credulous spirit of the modern type, as little disposed to examine what it receives as its ancient unreasoning predecessor, the development doctrines are doing much harm on both sides of the Atlantic, especially among intelligent mechanics, and a class of young men engaged in the subordinate departments of trade and the law. And the harm, thus considerable in amount, must be necessarily more than merely considerable in degree. For it invariably happens, that when persons in these walks become materialists, they become also turbulent subjects and bad men. That belief in the existence after death, which forms the distinguishing _instinct_ of humanity, is too essential a part of man’s moral constitution not to be missed when away; and so, when once fairly eradicated, the life and conduct rarely fail to betray its absence. But I have not, from any consideration of the mischief thus effected, written as if arguments, like cannon-balls, could be rendered more formidable than in the cool state by being made red-hot. I have not even felt, in discussing the question, as if I had a man before me as an opponent; for though my work contains numerous references to the author of the “Vestiges,” I have invariably thought on these occasions, not of the anonymous writer of the volume, of whom I know nothing, but simply of an ingenious, well-written book, unfortunate in its facts and not always very happy in its reasonings. Further, I do not think that palæontological fact, in its bearing on the points at issue, is of such a doubtful complexion as to leave the geologist, however much from moral considerations in earnest in the matter, any very serious excuse for losing his temper.