FUSION BY HEAT. 19 



quently bursting through them in various directions, forming 

 " dykes " and veins with numerous branches, from an inch to 

 hundreds of feet in diameter ; and, coming up frequently 

 through the entire thickness of the strata, it has flown over 

 the top, where it has, often in large masses, subsequently con- 

 solidated. These dykes are often found to contain imbedded 

 fragments of the identical rocks through which they appear 

 to have forced their passage in their upward movement. The 

 manner in which these fragments are imbedded, proves to a 

 demonstration, that the mass by which they are surrounded 

 was once in a fluid state, and that it subsequently became 

 solid, as we now find it. 



That the original fluidity of these injected rocks was pro- 

 duced by heat, is evident from the following, among other 

 considerations: 1. The crystaline character of some of these 

 rocks is such as could have been produced only by heat. 2. 

 The chemical effects produced upon the stratified rocks by 

 contact of the unstratified ones, are similar to those produced 

 by dykes of recent lava. 3. The different unstratified rocks 

 insensibly pass into each other, and indeed into modern lavas. 

 Besides, the mineral composition of the rocks, as well as the 

 form and position of the dykee, shows that their original 

 fluidity could not have been the result of water, which is the 

 only known natural element besides fire, to which their solu- 

 tion could possibly be attributed in any case. 



But as the rocks of w r hich we have spoken are primary 

 rocks, and serve as the basis of all stratified rocks in all places, 

 and as they must, therefore, have universally prevailed ove* 

 the surface of the earth before any other rocks were formed, 

 if their original state was that of igneous fluidity, it may be 

 assumed that such was the condition of the whole globe 

 that it was one vast ball of molten lava ! This is now gener- 



