. The ancient life-history of the earth; a comprehensive outline of the principles and leading facts of palæontological science. Paleontology. THE LAURENTIAN AND HURONIAN PERIODS. 6/ ancient metamorphic rocks of Bohemia and Bavaria may be regarded as being approximately of the same age. By some geological writers the ancient and highly meta- morphosed sediments of the Laurentian and the succeeding Huronian series have been spoken of as the " Azoic rocks" (Gr. a, without; zoe, life); but even if we were wholly destitute of any evidence of life during these periods, this name would be
. The ancient life-history of the earth; a comprehensive outline of the principles and leading facts of palæontological science. Paleontology. THE LAURENTIAN AND HURONIAN PERIODS. 6/ ancient metamorphic rocks of Bohemia and Bavaria may be regarded as being approximately of the same age. By some geological writers the ancient and highly meta- morphosed sediments of the Laurentian and the succeeding Huronian series have been spoken of as the " Azoic rocks" (Gr. a, without; zoe, life); but even if we were wholly destitute of any evidence of life during these periods, this name would be objectionable upon theoretical grounds. If a general name be needed, that of " Eozoic " (Gr. eos^ dawn ; zoe^ life), proposed by Principal Dawson, is the most appropriate. Owing to their metamorphic condition, geologists long despaired of ever de- tecting any traces of life in the vast pile of strata which con- stitute the Laurentian System. Even before any direct traces were discovered, it was, however, pointed out that there were good reasons for believing that the Laurentian seas had been tenanted by an abundance of living beings. These reasons are briefly as follows :—(i) Firstly, the Laurentian series con- sists, beyond question, of marine sediments which originally differed in no essential respect from those which were subse- quently laid down in the Cambrian or Silurian periods. (2) In all formations later than the Laurentian, any limestones which are present can be shown, with few exceptions, to be organic rocks, and to be more or less largely made up of the comminuted debris of marine or fresh-water animals. The Laurentian limestones, in consequence of the metamorphism to which they have been subjected, are so highly crystalline (fig. 21) that the microscope fails to detect any organic struc- ture in the rock, and no fos- sils beyond those which will be spoken of immediately have as yet been discovered in them. We know, however, of numerous cases in which
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