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552 ; and the third was the "Flora Fossilis Helvetiæ" in one volume, with seventy plates. He passed the winter of 1854-'55 in Madeira, on account of his health, and on his return from there published a paper on the fossil plants of that island, and another on the probable origin of the existing flora and fauna of the Azores, Madeira, and the Canaries. In this paper, and in a work published in 1860 on tertiary climates in their relation to vegetation, as well as in parts of his larger works on Switzerland, he propounded his theory of the existence of the Continent of Atlantis, during the Miocene period; a theory to which he held steadfastly for many years, but which the later soundings have shown to be extremely improbable in fact, and his own researches to be not needed to account for the phenomena of the distribution of plants and animals over the earth.

In 1 862 Heer examined the fossil flora of the lignites of Bovey-Tracy in Devonshire, and published a memoir upon them in the "Philosophical Transactions." At about the same time, he published a paper in the "Journal of the Geological Society" on certain fossil plants of the Isle of Wight. As his fame grew, fossils were sent to him in masses to be examined from all parts of the world; and we find among his papers notes on the cretaceous phyllites of Nebraska, the floras of Moletein in Moravia, Ruedlinburg in Germany, the Baltic miocene of Prussia, of the lignites of Zsélythales in Hungary, of Andö in Norway, and "Contributions to the Fossil Flora of Portugal." All of these works, important as they were in themselves, were only leading up to the great work of his life—the investigation of the Arctic fossil flora and the deduction from it of a satisfactory theory of the distribution of life over the earth. According to Dr. Gray, his first essay in this domain—which he has made so peculiarly his own—was in a paper on certain fossil plants of Vancouver Island and British Columbia, published in 1865; and in 1868 he brought out the first of the series of memoirs upon the ancient floras of Arctic America, Greenland, Spitzbergen, Nova Zembla, Arctic and Subarctic Asia, etc., which together make up the seven quarto volumes of the "Flora Fossilis Arctica," the last of which was finished only a few months before his death. According to M. de Saporta, he had been struck with the importance of the American element in what he called the Molassic flora of Switzerland. There was no question in it of vague analogies, but a number of dominant and characteristic species were represented by "homologues" or directly corresponding kinds now peculiar to North America, while there was nothing like them in Europe or the whole Eastern Continent, except as fossils. Among these plants were the sequoia of California, the cypress of Louisiana, the parasol palm of the Antilles, the tulip-tree, maples, and poplars, the European fossil forms of which were as like them as if they had been shaped upon living American trees as models. He saw in these resemblances, which implied that identical species were at some time in