Though typically developed in the great Canadian area already spoken of, the Laurentian Rocks occur in other localities, both in America and in the Old World.  In Britain, the so-called “fundamental gneiss” of the Hebrides and of Sutherlandshire is probably of Lower Laurentian age, and the “hypersthene rocks” of the Isle of Skye may, with great probability, be regarded as referable to the Upper Laurentian.  In other localities in Great Britain (as in St David’s, South Wales; the Malvern Hills; and the North of Ireland) occur ancient metamorphic deposits which also are probably referable to the Laurentian series.  The so-called “primitive gneiss” of Norway appears to belong to the Laurentian, and the ancient metamorphic rocks of Bohemia and Bavaria may be regarded as being approximately of the same age.

[Illustration:  Fig. 21.—­Section of Lower Laurentian Limestone from Hull, Ottawa; enlarged five diameters.  The rock is very highly crystalline, and contains mica and other minerals.  The irregular black masses in it are graphite. (Original.)]

By some geological writers the ancient and highly metamorphosed 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 detecting any traces of life in the vast pile of strata which constitute 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:—­(1) Firstly, the Laurentian series consists, beyond question, of marine sediments which originally differed in no essential respect from those which were subsequently 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 structure in the rock, and no fossils beyond those which will be spoken of immediately have as yet been discovered in them.  We know, however, of numerous cases in which limestones, of later age, and undoubtedly organic to begin with, have been rendered so intensely crystalline by metamorphic action that all traces of organic structure have been obliterated.  We have therefore, by analogy, the strongest possible