The ‶Introductory Address,″ which is usually delivered at the commencement of the Annual Session of most learned societies, is very properly intended to be of interest to all the members of the body before which it is given. Hence such addresses usually deal with the internal affairs of the Society itself, or are concerned with the current condition of the special science which the Society may happen to cultivate. That the custom here indicated is, in a general way, a good one, I cannot doubt. I am not, however, without the precedent of high authority in departing from this custom to-night; and I intend, therefore, rather to occupy your attention this evening with a few remarks upon a subject to which, it is true, I have been led by my own special studies, but which, nevertheless, has a general interest for all those who are engaged in the elucidation of geological phenomena. The subject upon which I have chosen to address you to-night concerns the conclusions which may be drawn by the palaeontologist from his study of the migrations of animals. This subject has been handled more or less fully by Sir Charles Lyell in his great work on the ‶Principles of Geology,″ and has also been incidentally treated of by Darwin in the ‶Origin of Species;″ whilst Barrande, Edward Forbes, De Verneuil, and other eminent palaeontologists have drawn attention to it in various portions of their works. In following such distinguished authorities, I do not propose to occupy your