60 CHEMISTRY OF THE KOCKS. 



the globe during all the time of the contraction and consolidation 

 of the lower elements. When every thing else that was conden- 

 sable had turned to dust and ashes and fallen to the earth, at last 

 the waters reached the parched and scorious surface and com- 

 menced that grand series of aqueous transformations which made 

 a new earth for the indwelling of life. 



In the first place it was necessary that the upper crust should 

 be hydrated, precisely as lime is slacked by pouring water on it. 

 The material which had been last deposited was in reality this 

 same caustic lime. In its lower deposits it was gradually inter- 

 mixed with the sillicious compounds, until these latter formed 

 without admixture the masses which are now the stratified gran- 

 itic rocks. As every one knows, the slacking of quicklime 

 absorbs a large quantity of water which is incorporated into the 

 solid as water of crystallization, and great heat is evolved with 

 enlargement of bulk. The pure silicious rocks do not take up 

 water in this way, being what is termed anhydrous. All the 

 rock-materials then that lie above the granite, must at some time 

 have undergone this hydrating, reheating and swelling process. 

 We accordingly find that all those strata which have remained 

 in their original position, such as gneiss, the mica schists, the 

 clay-slates, and the primary limestones, have the appearance of 

 having been subjected to great heat and pressure, after having 

 been acted upon by water and steam. In some instances they 

 have been partially melted, in others strangely contorted, and in 

 others partly dissolved. Under certain circumstances hot water 

 and steam will dissolve small portions of silica, and if charged 

 with carbonic-acid gas will dissolve lime quite freely. 



The rainfalls of the primeval ages must have been fully satu- 

 rated with the oxide of carbon which has played an important 

 part in the making up of the strata. In this form it carbonated 

 all the limestones, carried all the building-materials to the shell 

 and coral land-makers, and furnished the supplies for the immense 

 magazines of the hydro-carbons. And after all this there was 

 enough carbonic-acid gas left in the air for the enormous vegeta- 

 tion of the coal-beds. But it was necessary that the carbon of 

 this gas should be laid away in the earth in some form, either 



