National Geographic : 1956 Mar
+ This Banded Limestone, Canada's "Dawn Animal," Sparked a Scientific Clash In the alternate white and green bands of calcite and serpentine, Sir J. William Dawson, noted Canadian geologist, found microscopic evidence of what he believed to be the oldest known form of animal life. In the 1860's he named the fossil Eozoon canadense (dawn animal of Canada). His theory stirred a controversy that has continued to this day. Dissenting paleontologists classi fied Eozoon as of plant rather than animal origin. They described the white bands as calcite left by blue green algae, tiny seaweeds. Other scientists contended that the ancient "fossil" was purely mineral -a product of the heat and pressure of metamorphism. Today all sides agree on one point: Eozoon is not an animal colony of Foraminifera, as Dawson believed. A billion years old or more, it comes out of the Pre-Cambrian. © National Geographic Society Staff Photographers B. Anthony Stewart (left) and Willard R. Culver 377 Entombed Shells + Shine in Lumachel This piece of fossiliferous limestone, also known as fire marble, comes from the prov ince of Carinthia, Austria. When polished, its surface emits rainbow hues from fos sil shells that have retained their mother-of-pearl sheen more than 150 million years. Limestone, most often formed by the deposition of the skeletons of marine in vertebrates, is chalk-white in its pure state. Color reveals the presence of impurities. Iron oxide, for example, may tint the stone brown, yellow, or red. Here the dark back ground denotes carbon. Samples of silicified wood at bottom show the colors of other minerals. Left: Fossil oak from Washington State. Right: Spruce from Idaho.