This idea, that the sea and not the land has changed its level, was generally held at the time Lamarck wrote, though Strabo had made the shrewd observation that it was the land which moved. The Greek geographer threw aside the notion of some of his contemporaries, and with wonderful prevision, considering the time he wrote and the limited observations he could make, claimed that it is not the sea which has risen or fallen, but the land itself which is sometimes raised up and sometimes depressed, while the sea-bottom may also be elevated or sunk down. He refers to such facts as deluges, earthquakes, and volcanic eruptions, and sudden swellings of the land beneath the sea. "And it is not merely the small, but the large islands also, not merely the islands, but the continents which can be lifted up together with the sea; and, too, the large and small tracts may subside, for habitations and cities, like Bure, Bizona, and many others, have been engulfed by earthquakes."[75] But it was not until eighteen centuries later that this doctrine, under the teachings of Playfair, Leopold von Buch, and Élie de Beaumont (1829-30) became generally accepted. In 1845 Humboldt remarked, "It is a fact to-day recognized by all geologists, that the rise of continents is due to an actual upheaval, and not to an apparent subsidence occasioned by a general depression of the level of the sea" (_Cosmos_, i). Yet as late as 1869 we have an essay by H. Trautschold[76] in which is a statement of the arguments which can be brought forward in favor of the doctrine that the increase of the land above sea level is due to the retirement of the sea.[77] As authentic and unimpeachable proofs of the former existence of the sea where now it is absent, Lamarck cites the occurrence of fossils in rocks inland. Lamarck's first paper on fossils was read to the Institute in 1799, or about three years previous to the publication of the _Hydrogéologie_. He restricts the term "fossils" to vegetable and animal remains, since the word in his time was by some loosely applied to minerals as well as fossils; to anything dug out of the earth. "We find fossils," he says, "on dry land, even in the middle of continents and large islands; and not only in places far removed from the sea, but even on mountains and in their bowels, at considerable heights, each part of the earth's surface having at some time been a veritable ocean bottom." He then quotes at length accounts of such instances from Buffon, and notices their prodigious number, and that while the greater number are marine, others are fresh-water and terrestrial shells, and the marine shells may be divided into littoral and pelagic.