. Cold-blooded vertebrates: part I. Fishes. Fishes; Amphibians; Reptiles. FOSSIL TRACKS AND TRAILS about nine feet. In these tracks the imprints themselves are not preserved, but only their natural casts. It seems that the animal walked over the soft earth which immedi- ately overlay a peat bed, and that this earth was in turn covered by a thick layer of sand, which filled in the deep footprints. In the ages that followed, the sand became. Fig. 76. Tracks of Iguanndon, much reduced. From Wealden strata, England. Modified from Hutchinson consolidated into the heavy band of sandstone that we see
. Cold-blooded vertebrates: part I. Fishes. Fishes; Amphibians; Reptiles. FOSSIL TRACKS AND TRAILS about nine feet. In these tracks the imprints themselves are not preserved, but only their natural casts. It seems that the animal walked over the soft earth which immedi- ately overlay a peat bed, and that this earth was in turn covered by a thick layer of sand, which filled in the deep footprints. In the ages that followed, the sand became. Fig. 76. Tracks of Iguanndon, much reduced. From Wealden strata, England. Modified from Hutchinson consolidated into the heavy band of sandstone that we see today. When the coal is mined out, the soft, uncon- solidated layer containing the tracks cleaves from the underside of the sandstone and leaves the natural casts of the tracks protruding below the general level of the sand- stone roof of the mine. It is thus that the trail of the dino- saur has been revealed to us of the present day. The great antiquity of fossil footprints is nowhere more clearly and convincingly demonstrated than in the Grand Canyon of the Colorado, in Arizona. This area, now set aside as a national park, was in several periods, each separated from the next by millions of years, inhabited by large and varied assemblages of animals, none of which resembled any of the creatures living there today. Fossil tracks and trails preserved at levels hundreds of feet apart in the rock walls of the canyon furnish the evidence for this statement. At the time the tracks were made there [ ^75 ]. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hildebrand, Samuel F. (Samuel Frederick), 1883-1949; Gilmore, Charles Whitney, 1874-; Cochran, Doris M. (Doris Mable), 1898-1968. [New York, Smithsonian institution series, inc. ]
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Keywords: ., bookcentury1900, booksubj, booksubjectfishes, booksubjectreptiles
