past ages diffused simultaneously through both continents, indications of ancient territorial connections. The substitution of the hypothesis of a common origin of life at the poles and its diffusion by migrations to the southward over all the continents, for the theory of Atlantis, which he had expounded in his earlier works, was of gradual growth, and was the direct result of his examinations of the Arctic fossil flora. In this he was struck by the abundance of the species of a southern and even tropical character, which he found in beds reaching far up toward the extreme north. On the evidence of such fossils was built the theory of a warm, moist climate prevailing in the Arctic as well as in the temperate and sub-tropical regions during the Tertiary period, which, suggested by Heer, has been and elaborated by De Saporta, and is avowed by Dr. Gray.
Heer never accepted the Darwinian theory of the origin of species by variation and natural selection. To it he objected, in general, that no new species had arisen within human knowledge; that no transitional forms had been discovered anywhere; and that it was inconsistent with the progress from simpler to more highly organized beings which he conceived to be the rule of development. To account for the changes that had evidently taken place during geological history, he supposed that, at certain undetermined epochs, species underwent changes, the completion of which occupied only a relatively short time, to be again consolidated and continue unchangeable till the moment when another crisis should bring on a new recasting.
The delicate health which marked his life during the period in which he was best known to science prevented Heer's making extensive explorations in person. Most of his time was spent in his study, examining the collections submitted to him by stronger and more active men, and more capable of enduring the fatigues of such works. But it is to him, M. de Saporta remarks, that we are indebted for our knowledge of the meaning of what such men discovered. Without him, active to his last hour, it would have taken a very long time for phytologists, in the absence of any concert of understanding, to accomplish the summarizing of their aggregate work which he did so successfully, and with so much clearness and intelligence. He was a sufferer from pulmonary disease, and during the last twelve years of his life did much of his work in bed, having his papers and specimens arranged upon a table before him, while his daughter acted as his scribe. Having finished the last volume of his "Fossil Arctic Flora" in the summer of 1883, he was taken to a sheltered retreat on Lake Geneva, for the recovery of his exhausted strength; and he died at his brother's house. It is said of him by his biographer in "Science," and repeated by Dr. Gray, that "a man more lovable, more sympathetic, and a life more laborious and pure, one could scarcely imagine."
