_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.
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