Page:Popular Science Monthly Volume 3.djvu/453

Rh As might be expected, there was a group of Crustaceans, animals who frequent the mud left at low tide. Their impressions have been left on the rocks from the dawn of the Paleozoic age to the very latest period. The famous Prototichnites of Canada upon the Potsdam sandstone, so ably described by Logan and Owen, are generally thought to have been made by gigantic representatives of this class, though hardly by the Pterogotus form, as suggested by Salter and Woodward, because the latter were exclusively swimming animals. The Prototichnites were not represented in the Trias. The forms preserved at Amherst are peculiar, and not to be referred to any special order of Crustacea. One was a giant with a track-way 27 yards wide, and the idea suggested by its inspection is that of an animal with small body stilted high upon very long legs.

Other species of Ichnozoa may have been Annelids, Avith their sinuous, fimbriated line of march, worms, mollusks, with single, double, or treble depressed lines, and various larval forms—whether like those crawling over the surface or making burrows in the mud. A square rod of this Triassic surface will be as thoroughly carved by these various impressions, produced by the lower orders of animal life, as the same surface of the sea-shore in temperate or tropical climes at the present day.

Thus this brief review of the different classes of Triassic Ichnozoa shows a natural assemblage, such as might be found associated in maritime districts. The huge birds associated with kangaroodike forms reminds us immediately of the modern Australian realm, with the cassowaries and the long list of marsupials. Indeed, it would not be strange if the assemblage of life which first showed itself in the American Triassic estuaries had gradually migrated eastward over regions now covered by the Northern Atlantic, pushing farther and farther in each g-eoloscical era till the ultima Thule of Australia is reached, where the modern representatives of the Ichnozoa were prevented from further migration by the termination of continental areas. Soon after its occupation, Australia must have been separated from the Asiatic Continent by a partial submergence, so that the peculiar fauna became restricted, and none of the animals could retrace their steps toward the setting sun, even if they desired. It may be, then, that historic Australia represents Triassic New England in its faunal peculiarities—terrestrial, but not maritime, since marine animals cannot so easily be restricted in their migrations or developments.

Besides footprints, other markings on the Connecticut sandstone attract our attention. We observe the marks of rain-drops, ripples of the waves, shrinkage-cracks, broken bubbles arising from marsh-gas, septaria, rarely a shell, a possible echinoderra, coprolites of birds as determined by chemical analysis, a few reptilian bones, bark and cones of gymnosperms, besides other curious marine and terrestrial plants, remain.