68 THE DOCTRINE OF DESCENT. 



clayey, and chalky rocks alternate with one another, al- 

 ready 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 Forami- 

 nifera, which exclude any other interpretation than that 

 of a living being resembling the low Foraminifera. This is 

 of great significance, as the profusion of life met with in 

 the Silurian and Devonian strata presupposes an im- 

 measurably long antecedent period during which life 



