Ch. XL] THE PRIMARY ROCKS. 213 



rocks have been produced from the accumulated debris or 

 detritus of older rocks, transported and arranged by the 

 action of water after the same manner as beds of sand, clay, 

 and calcareous substances, now actually forming in lakes, 

 rivers, and the ocean : whilst the origin of the unstratified 

 rocks, on the other hand, is attributed to the agency of an 

 internal fire, which, according to various physical evidences, 

 appears to exist in the centre of the earth ; and to hold there 

 an undisputed sway, converting all matter within its influence 

 into a state of fluidity. 



Some modern geologists, like Leibnitz and others of old, 

 carry back their speculations to a period when the whole 

 earth was, as they suppose, one element of liquid fire ; and 

 are of opinion that the granitic rocks have resulted from the 

 cooling and consolidation of this ignited mass ; that this 

 refrigeration has been gradual, and is still in progress, whereby 

 the crust or solid shell of the Earth is continually augmenting 

 in thickness. 



Now, if this conclusion be correct, and the data from which 

 it has been deduced render it not improbable, the whole mass 

 of granite is made up of successive or concentric layers, each 

 of which is refer rible to a distinct period of time. This 

 second refrigeration, however, although progressive, is not 

 supposed to have been always uniform in its operation, the 

 melted mass having been, from some unknown causes, subject 

 to periodical disturbances, by which it has burst through the 

 incumbent solid rocks, and been protruded in various forms, 

 according to the peculiar circumstances of the catastrophe. 

 These forms, infinitely varied as they are, when we descend 

 to minute distinctions, may be arranged under three heads : 

 first, those that have resulted from fused masses which have 

 not reached the surface of the earth ; secondly, those that 

 have been poured out at or near the surface, but at the same 

 time exposed to a great superincumbent pressure; lastly, 

 those derived from the fused mass whilst in free communica- 

 tion with the surface, either under water or in the atmosphere, 



p 3 



