The new line of investigation thus opened by the French naturalists was followed up by the Norwegian, Sars, in 1835, by Edward Forbes, in our own country, in 1840,[4] and by Oersted, in Denmark, a few years later.  The genius of Forbes, combined with his extensive knowledge of botany, invertebrate zoology, and geology, enabled him to do more than any of his compeers, in bringing the importance of distribution in depth into notice; and his researches in the Aegean Sea, and still more his remarkable paper “On the Geological Relations of the existing Fauna and Flora of the British Isles,” published in 1846, in the first volume of the “Memoirs of the Geological Survey of Great Britain,” attracted universal attention.

[Footnote 4:  In the paper in the Memoirs of the Survey cited further on, Forbes writes:—­

“In an essay ’On the Association of Mollusca on the British Coasts, considered with reference to Pleistocene Geology,’ printed in [the Edinburgh Academic Annual for] 1840, I described the mollusca, as distributed on our shores and seas, in four great zones or regions, usually denominated ‘The Littoral zone,’ ‘The region of Laminariae,’ ’The region of Coral-lines,’ and ‘The region of Corals.’  An extensive series of researches, chiefly conducted by the members of the committee appointed by the British Association to investigate the marine geology of Britain by means of the dredge, have not invalidated this classification, and the researches of Professor Loven, in the Norwegian and Lapland seas, have borne out their correctness The first two of the regions above mentioned had been previously noticed by Lamoureux, in his account of the distribution (vertically) of sea-weeds, by Audouin and Milne Edwards in their Observations on the Natural History of the coast of France, and by Sars in the preface to his Beskrivelser og Jagttayelser.”]

On the coasts of the British Islands, Forbes distinguishes four zones or regions, the Littoral (between tide marks), the Laminarian (between lowwater-mark and 15 fathoms), the Coralline (from 15 to 50 fathoms), and the Deep sea or Coral region (from 50 fathoms to beyond 100 fathoms).  But, in the deeper waters of the Aegean Sea, between the shore and a depth of 300 fathoms, Forbes was able to make out no fewer than eight zones of life, in the course of which the number and variety of forms gradually diminished until, beyond 300 fathoms, life disappeared altogether.  Hence it appeared as if descent in the sea had much the same effect on life, as ascent on land.  Recent investigations appear to show that Forbes was right enough in his classification of the facts of distribution in depth as they are to be observed in the Aegean; and though, at the time he wrote, one or two observations were extant which might have warned him not to generalize too extensively from his Aegean experience, his own dredging work was so much more extensive and systematic than that of any other naturalist, that it is not wonderful he should have felt justified in building upon it.  Nevertheless, so far as the limit of the range of life in depth goes, Forbes’ conclusion has been completely negatived, and the greatest depths yet attained show not even an approach to a “zero of life":—­