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memoirs published by the officers of the Survey, to the beautifully illustrated 'Decades,' in which Prof. Forbes's artistic skill and judgment are so manifest; his Monograph on the British Naked-eyed Medusæ, published by the Ray Society; and the large work on the 'Natural History of the British Mollusca' undertaken and finished in conjunction with Mr. Hanley—are sufficient evidence that his active mind was not one of those which are oppressed and overpowered by details.
Among these many contributions to science there are two so marked by originality and genius, so pregnant with results for the future, as to deserve more than passing notice. The first of these is the 'Essay on the Distribution of the Fauna and Flora of the British Isles' in the first volume of the Memoirs of the Survey, which may be characterized as one of the happiest applications of the facts of one science to the elucidation of the difficulties of another that has ever been made. The doctrine laid down in this memoir is, that the existing distribution of animals and plants can only be regarded, not as a primary and independent phenomenon, but as the result of previously existing conditions,—as the product, in fact, of two factors; the one, the successive changes of living beings in time; the other, the successive changes of the position and boundaries of land and sea in space.
The second work here adverted to is that remarkable Essay on the Tertiary Beds of the Isle of Wight, the fruit of Prof. Forbes's last labours.
By an elaborate study of the Purbeck beds in Dorsetshire in 1850, Prof. Forbes had come to the unexpected conclusion that they were divisible into three formations, each characterized by distinct sets of fossil remains; and that the freshwater mollusca and foraminifera of the Purbeck beds, to which he had given his more particular attention, did not agree specifically with the fossils of the incumbent Hastings Sands. The latter he proposed to class as Lower Cretaceous or Neocomian, while the Purbeck he henceforth considered as an uppermost member of the Oolitic group. His great success in these researches awakened in him a lively curiosity to examine in like minute detail the great series of tertiary freshwater strata occurring in the northern part of the Isle of Wight. Accordingly, he devoted several months in the autumn and winter of 1852 to the
