Page:Popular Science Monthly Volume 67.djvu/571

Rh three-toed horses, including (1) those with excessively light, almost deerlike limbs; (2) others with shorter, more robust limbs, less specialized and leading apparently into the true modern horse; (3) others again, forest living forms, with spreading side toes, perhaps designed to prevent the animals from sinking into the soft ground of the swampy regions which they may have inhabited. Here also was found the complete skeleton of the camel, Camelus occidentalis, of mastodons, and of several other new types of animals, especially the wolves and foxes of the period.

Another American Museum expedition worked its way into the waterless desert in western South Dakota, where, in the bed of an

ancient inlet of the sea, perhaps ten million years ago, were deposited the skeletons of two well-known varieties of sea reptiles, mosasaurs and plesiosaurs. These were found encased like mummies in a soft rock imbedded in larger concretions which stood up like mushrooms in what the westerners called a 'blow-out.' Numerous skeletons were found in a beautiful state of preservation, and formed the chief feature of this expedition. Just as Mr. Barnum Brown, the head of this party, was on his way east, a telegraphic order directed him into northwestern Arkansas to a comparatively recent deposit, perhaps 200,000 years of age, made just prior to the glacial period. It recorded chiefly the small western preglacial fauna, the field mice, shrews, minks, badgers, rabbits, ancestors of familiar living western types, mingled, however, with remains