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 primaeval 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. The remains 

 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 

 body, 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- 



