518 



Scientific Geulogy. 



Theory of the Sufficiency of Causes now in action, with no increase 

 of intensity, to account for Geological Phenomena. 



Although the theory of central heat has been so generally adopted 

 as to excite at present but little discussion, yet a theory is now in the 

 course of a full and able development by a distinguished geologist,* 

 relating to the dynamics of existing causes, which seems likely to 

 elicit much of talent and feeling in its examination. He maintains 

 that if the causes now in operation be supposed to have acted during 

 immense periods of past time, without any increase of intensity, they 

 may have produced all the phenomena which the records of geology 

 disclose. Those who take the opposite ground are ready to admit 

 that the dynamics of existing causes has been greatly underrated ; 

 nor do they suppose that any causes different in their nature from ex- 

 isting ones have been in operation in past times. But they suppose 

 these causes to have acted with far greater intensity formerly than at 

 present: and they appeal to the following facts in support of this 

 opinion, and in opposition to the theory above stated. 



1. The spheroidal figure of the earih renders it probable that it 

 was once fluid. Whether this fluidity was igneous or aqueous, the 

 operation of fire or water must have been far more powerful formerly 

 than at present. 



2. Perhaps nine tenths of our present continents exhibit evidence 

 that their stratified rocks were formed beneath the ocean ; and they 

 must consequently have been subsequently elevated ; and this, not by 

 little and little, but by a few paroxysmal efforts of volcanic force. But 

 that force, during the last 4000 years, seems to have been by far too 

 feeble to produce effects to be compared with the elevation of a conti- 

 nent, or even a single mountain chain. 



3. The products of volcanic agencies in early times, that is, the 

 unstratified rocks, appear to have been far more abundant than dur 

 ing the last few thousands of years. That is, the deposits of gran- 

 ite, sienite, and porphyry, whose cotemporary production can be ren- 

 dered probable, are of greater extent than those of basalt, greenstone, 

 and trachyte ; and these latter more abundant than the lavas of ex- 

 isting volcanoes : thus exhibiting a diminishing energy of volcanic 

 action. 



4. A correspondent decrease of violence in this power, obvious 

 in the disturbances and dislocations of the stratified rocks by the pro- 



♦Principles of Geology by Charles Lyell Esq. Vol. 1. London 1830 : Vol. 2 

 London 1832: Vol 3, forthcoming-. 



