874 THE WONDERS OF GEOLOGY. Lect. VIII. 



phenomena into consideration, together with the facts pre- 

 viously stated, of the transmutation of one substance into 

 another by the effect of caloric, it appears to me, that in 

 the present state of our knowledge we are warranted in 

 concluding, that all the granite and associated plutonic 

 rocks that are accessible to human observation, are nothing 

 more than sedimentary deposits altered by igneous agency. 

 But from what source were the most ancient granitic 

 rocks derived — whence originated the materials upon which 

 igneous action exerted its influence, and produced those 

 crystalline masses which are the Ultima Thule of geological 

 research ? Was granite, as Humboldt has supposed, the 

 basis or framework upon which the first aqueous sediments 

 were deposited ? — These are questions which in the present 

 state of our knowledge we are not in a condition to solve ; 

 and it does not appear probable, that vestiges of the first 

 dawn of creation upon the surface of our planet will ever 

 be revealed to mortal eye. 



37. Organic Remains in the Metamorphic Eocks ? ? 

 — I have stated, that with the lowermost of the slate rocks, 

 all traces of organization are lost ; but this assertion re- 

 quires some reservation, for, as an eminent geologist has 

 remarked, " with the exception of granite, probably no 

 rock is known beneath which organic remains may not be 

 found."* Let us here resume the inquiry. 



From the intense heat to which the metamorphic rocks 

 have been exposed, we cannot, of course, expect to find any 

 organic remains, except such as are formed of materials 

 capable of resisting the effects of that influence. The ob- 

 servations and experiments of the Rev. J. B. Reade have 

 shown, that vegetables possess a structure which is com- 

 posed of silex, and is indestructible in a common fire.f In 



* Macculloch's Western Isles, p. 514. 



f See Appendix, to this volume, C, for Mr. Keade's observations and 

 experiments on this subject. 



