THEORY OF THE EARTH. 423 



ther form to the earth, previous to the last partial re- 

 volutions. That chapter was written at the very re- 

 mote period already mentioned, and printed long ago: 

 the present views are the result of further reflection 

 on materials not then satisfactorily understood. 



I have shown that some of the chief lignite deposits 

 must have been produced in the same manner as the 

 inferior coal, and are now lying where the generating 

 plants grew. To form a true theory of the following 

 conditions of the Earth, we ought to be certain of the 

 number of these, according to superposition, or geolo- 

 gical place. I think we are quite sure of but two; in 

 the oolithe, and in the green sand : and if I can build 

 on those, I am therefore limited to them. But we can 

 now see how indispensable an accurate knowledge of 

 all the coal deposits of the world is, to a Theory of 

 the Earth. If the inferior coal, for example, were li- 

 mited to Britain, or the two great lignites to Europe, 

 the conditions of the earth, inferred from these, would 

 be partial only, as well as the revolutions: whence, 

 until every coal, of whatever nature, in the world, is 

 thoroughly known and accurately compared, we must 

 remain in ignorance, as well of the number as the na- 

 ture, of the conditions and revolutions engaged in this 

 long interval. Hence the wider and important consi- 

 deration that follows, hitherto overlooked by geology. 

 If any revolution engaged in any of these coal deposits 

 was universal, such a coal should correspond in geo- 

 logical time, all over the world, and thus be an "uni- 

 versal formation ;" since we are sure that it was formed 

 on the surface, be the associated strata what they may. 

 And if the facts should prove such as to render this 

 belief impossible, then the different parts of the world, 

 producing coal at different times, have been under dis- 

 tinct revolutions and conditions, of a partial nature. 



