CHAPTER II 

 Transformations of Land and Water 



NOWHERE have we been able to reach the primary solidified 

 crust of the earth. For a long time it was believed that 

 this crust was represented by rocks which, in part, date back to 

 a very great antiquity, such, for instance, as the granitoid and 

 the gneisses, forming, almost of themselves, enormous areas such 

 as the central plateau of France. It has, however, been shown 

 that, in spite of appearances to the contrary, we have here, too, 

 simply rocks deposited by water, and not all of the same age. 

 Though some of them are to be classed with the oldest rocks 

 known, others, identical in their mineralogical constitution 

 and structure, are more recent and are discovered at different 

 levels in analogous conditions. When the rocks laid down 

 horizontally as sediment were folded by lateral pressure, it 

 was near the bottom of these concave folds that granitoid rocks 

 belonging to the same age as the sedimentary beds were found. 

 From this we may infer that they were the result of a trans- 

 formation of sedimentary rocks in a partly molten state 

 violently compressed, and more or less altered either by gaseous 

 or liquid infiltrations, and, through this two-fold action, 

 crystallized. We call these rocks metamorphosed ; and meta- 

 morphosis is of very general occurrence. It caused the formation 

 of gneiss and granite whenever sedimentary rocks were com- 

 pressed and folded, so that rocks once called primitive are seen 

 to have lost that quality. 1 



It is none the less true that the oldest portions of the globe 

 now emergent consist essentially of these rocks, whose thickness 

 in certain places is more than fifteen thousand metres. This fact 

 alone enables us to gauge the time required for such deposits 

 to be laid down, especially if we consider that these deposits, 

 by no means compact at first, have achieved the homogeneity 

 which we find in gneiss. 



1 VI, 172. 



