68 THE DOCTRINE OF DESCENT. 
groups were formerly comprised under the name of 
Transition rocks, or Graywacke formation. In them 
also sandy, clayey, and chalky rocks alternate with one 
another, already exhibiting modifications of a local 
nature, from which, towards the carboniferous period, 
issued the first beginnings of continental upheaval. 
The granite, gneiss and slate, which as primary rocks, 
or primitive formations, originated before the Silurian 
rocks, are for the most part sediments of hot or very 
warm primeval seas, which have undergone manifold 
internal changes from pressure and heat. Till recently, 
they were likewise termed the Azoic group, as contain- 
ing no vestiges of life, when the discovery of the 
Eozoon and its unlimited occurrence in the Laurentian 
strata of Canada, proved that the required conclusion to 
the series had actually taken place. 
With this Eozoon we begin the enumeration of the 
antediluvian animals from below upwards. Theremains 
of this creature consist of a more or less irregular system 
of chambers with cretaceous walls, of which the interior 
is filled with serpentine or pyroxene. It was attempted 
to deny the organic origin of this cretaceous testa, which 
may best be compared to the shells of the Foraminifera. 
But renewed researches have substantiated that although 
in the great mass of the Eozoon rocks occurring in vast 
strata, metamorphosis has rendered it nearly, if not 
quite, impossible to recognize the true nature of the 
hody, pieces here and there occur with the chambering 
so distinctly marked, and a tubular structure peculiar 
to the Foraminifera, which exclude any other interpre- 
tation than that of a living being resembling the low 
Foraminifera. This is of great significance, as the pro- 
