. Dawn of life: being the history of the oldest known fossil remains, and their relation to geological time and to the development of the animal kingdom. Paleontology; Eozoon; Life. 06 THE DAWN OF LIFE. Thus we have^ in the natural state^ the walls of car- bonate of lime and the cavities empty. When fossil- ized the cavities may be merely filled with carbonate of lime, or they may be filled with silica ; or the walls themselves may be replaced by silica and the cavities may remain filled with carbonate of lime; or both, the walls and cavities may be represented by or filled with silica or sili
. Dawn of life: being the history of the oldest known fossil remains, and their relation to geological time and to the development of the animal kingdom. Paleontology; Eozoon; Life. 06 THE DAWN OF LIFE. Thus we have^ in the natural state^ the walls of car- bonate of lime and the cavities empty. When fossil- ized the cavities may be merely filled with carbonate of lime, or they may be filled with silica ; or the walls themselves may be replaced by silica and the cavities may remain filled with carbonate of lime; or both, the walls and cavities may be represented by or filled with silica or silicates. The ordinary specimens of Eozoon are in the third of these stages, though some a ind If«» » i! I >»»»«f ;C 'â /â ///y^\. a Fig. 22. Diagram showing different States of Fossilization of a Cell of a Tabulate Coral. a.) Natural conditionâwalls calcite, cell empty, (b.) Walls calcite, cell filled with the same, (c.) Walls calcite, cell filled with silica or silicate, (d.) Walls silicified, cell filled with calcite. (e.) Walls silicified, cell filled with sihca or silicate. exist in the second, and I have reason to believe that some have reached to the fifth. I have not met with any in the fourth stage, though this is not uncommon in Silurian and Devonian fossils. With regard to the calcareous organisms with which we have now to do, when these are imbedded in pure limestone and filled with the same^ so that the whole rock, fossils and all, is identical in composition, and when metamorphic action has caused the whole to become crystalline, and perhaps removed the remains of carbonaceous matter, it may be very difficult to. 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 Dawson, John William, Sir, 1820-1899. London, Hodder & Stoughton
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