Page:Popular Science Monthly Volume 74.djvu/354

350 was no haste in publication; aside from some very brief communications to societies, nothing appeared until 1839, when the Journal of Researches was printed. Owen's descriptions of the fossil mammalia was issued in 1840 with an introduction by Darwin and the final publication of results was made in three parts, dated 1842, 1844 and 1846. Thus early in his career, Darwin showed that caution which characterized him throughout life, an indifference to priority which was the outgrowth of his love of accuracy.

Part 2 of the "Geological Observations," dated 1844, relates chiefly to volcanic islands. In most cases the stay at those was brief and the studies were fragmentary; yet Darwin saw enough to let him discuss the origin of volcanic cones, to determine some cardinal points respecting the distribution of the islands, to distinguish submarine from subaerial lava flows and to prove that experimental studies on metamorphosis of limestones had led to very nearly true conceptions of the process.

As the coast survey of southern South America was the important object of Captain Fitzroy's expedition, there was ample time for a good reconnaissance of that region and Darwin spent nearly six months in studying the pampas from the Parana and Uraguay rivers southward almost to Magellan's Strait. A synopsis was given as an introduction to Owen's Memoir, but the details did not appear until 1846, when they were published as Part 3 of the "Geological Observations." The whole subject was discussed attractively in the second edition of the Journal of Researches.

The superficial deposit of the great plains is a "reddish argillaceous earth" containing concretions of indurated marl, which, at times become continuous layers or even replace much of the red earth. In the northerly part of the plains-area, this pampas deposit, which passes downward into sands, limestones and clays of late Tertiary age, yielded no marine shells to Darwin; its infusoria, studied by Ehrenberg, proved to be partly marine, partly freshwater, while the marly concretions resemble some freshwater limestones seen in Europe; but this paucity of invertebrate life was unimportant, for the whole of that region proved to be one vast cemetery, in which the skeletons of gigantic extinct mammals are so numerous that a line could not be drawn in any direction without passing through some bones. In northern Patagonia the red deposit is bound closely to an overlying gravel, containing marine forms belonging to species now existing on the coast, while in southern Patagonia marine shells occur in the pampas deposit itself.

Darwin believed that this pampas material was deposited within a vast estuary, into which great rivers carried from the surrounding region carcasses of the animals whose skeletons were entombed in