ANTIQUITY OP THE METAMORPHIC SYSTEM. 81 



of metamorphism, so it is among them that the geologist 

 often meets with his greatest doubts and difficulties. Defin- 

 ing them as the metamorphic, they were at one time regarded 

 as preceding the fossiliferous strata, and as marking a period 

 of the earth's history when life did not exist, and when, of 

 course, its reliquiae were not expected to be found in the 

 rocky strata. As research extended, fossils were here and 

 there .discovered, even in these metamorphic strata ; and 

 hence the necessity of arranging them (see Sketch No. 5) 

 according to this new evidence into "systems" and "for- 

 mations," as had been done with the younger and more 

 fossiliferous strata. But beyond the deepest in which traces 

 of life have been detected, there still lie vast masses of 

 crystalline and granite-looking schists unresolved, and ap- 

 parently unresolvable, and to such the designation " meta- 

 morphic " is still specially applicable, and may ever remain 

 so. In these we find no legible record of world-history : 

 nothing beyond the great facts that they are stratified rocks, 

 and must have been laid down in seas and estuaries like all 

 other sediments, and that millions of ages must have elapsed 

 during their slow conversion from silts and sands and 

 gravels to crystalline schists and granitoid masses. But 

 though this be the present state of geologic knowledge, we 

 dare not, looking at the progress of the past, presume that 

 further discoveries will not be effected. These old rocks 

 may yet tell their tale of life just as the Laurentian and Cam- 

 brian have done it before them ; for, carry our researches 

 backward as we may, we perceive no traces of a beginning, 

 any more than in the existing operations of nature we see 

 indications of an end. 



Once more : let it be clearly understood that metamor- 

 phism is simply internal mineral change ; that under pres- 

 sure, heat, chemical action, and other kindred forces, all 

 rock-matter in the earth's crust is incessantly undergoing 



F 



