332 THE TRANSFORMATIONS OF THE ANIMAL WORLD 



truly stupefying discoveries ? One alone Coffers j 

 itself, and that with irresistible conviction. The 

 pre-Cambrian world was already a very old one, 

 and its discovery does not bring us much nearer to 

 the beginning of life on the earth than did the 

 memorable discoveries of Murchison, Barrande, and 

 Dr. Hicks, in the more and more distant zones of the 

 Silurian and Cambrian strata of the Old World. We 

 are condemned to descend much lower still through 

 the enormous thicknesses of the oldest sediments. 



But here we find ourselves arrested by an almost 

 insurmountable difficulty. Wherever it is possible 

 to observe the base of the pre-Cambrian strata, 

 they are seen to rest on a soil of which the mode 

 of formation for a long time remained enigmatical, 

 and which was prematurely described by the name 

 primitive soil, on the hypothesis that it resulted 

 from the consolidation of a thin but solid crust 

 upon the surface of the terrestrial globe, itself in 

 a state of igneous fusion. This soil is essentially 

 composed of mica, schist, and gneiss, amongst 

 which are sometimes intercalated bands of crys- 

 talline limestone, or amphibolites, rich in lime and 

 magnesia. All these rocks offer a dual character, 

 being composed, on the one hand, of, perfectly 

 crystalline silicated minerals, which from a chemical 

 and mineralogical point of view assimilate them 

 to the eruptive rocks of the granite family ; but, 

 on the other, the elements of these rocks have a 

 clearly foliated structure quite similar to that of 

 the most normal sedimentary rocks. By^reason 

 of this double modality, a Belgian geologist, 

 d'Homalius d'Halloy, proposed nearly a century ago 



