Since the researches of Heer into the Miocene Flora of Switzerland have invested the theory of a Tertiary Atlantis with some degree of probability, other observers have come forward with arguments on the one hand which lend support to that hypothesis; whilst on the other hand it has been attempted to prove that the facts (as to the presumed migrations of plants and animals) are to be accounted for rather by a connection between Europe and America through the Asiatic region. My examination of the Jamaican fossils first led me to support a modification of the original view taken by Heer, and in April, 1866, I communicated to the Geological Society a paper bearing on the subject. That paper was read on the 20th of June, 1866, and an abstract of it appeared in the August number of this Magazine. I propose, on the Present occasion, to make a few remarks on the probility of the former connection between the eastern and western shores of the Atlantic.