THEORY OF THE EARTH. 429 



there are some imperfections, the essential facts are 

 matter of undisputed Evidence. 



There can he nothing in the nature of Revolution, 

 strictly speaking, till the third condition, in which it 

 is presumed that the unequal expansions of the in- 

 terior fluid where producing mountains during the 

 progress of cooling: while I must here mark, as 

 evidence of such a proceeding, that the Moon presents 

 this very character; being evidently a glohe with a 

 solid irregular surface most obviously produced in 

 this manner, at very different periods, without stratified 

 rocks, and, thence, rocky through the cooling of 

 fluids alone; while the evidence, not merely for the 

 fact, but for the progression, and for its very cause, is 

 seen in its volcanoes, successively produced, and still 

 occasionally active. 



If such expansion, with effusion of igneous rocks, is 

 thus the cause of the subsequent Revolutions, so, from 

 the third form of the earth onwards, it becomes de- 

 monstrated, and as to each successive one, with some 

 hesitation perhaps as to the lignites, by facts which no 

 philosophical geologist now disputes, though I have 

 here multiplied the number; yet, in no Case, without 

 the same evidence. It is sufficient to say, that the 

 immediate demonstration rests in the volcanic rocks, 

 and in the effects of their powers on the stratified 

 ones ; and that the various analogies, both in the pro- 

 duce and in the effects, extend this absolute and visible 

 evidence, retrogressively, though the whole system. 

 Where that evidence was formerly doubtful or dis- 

 puted, I have now also completed it; by tracing the 

 whole of the expansive actions backwards from the 

 Coral islands, and by showing that there are a suf- 

 ficient number of distinct productions of igneous 

 rocks; succeeding each other at intervals of time, to 



