THEORY OF THE EARTH. 455 



periods, or the order, have been: hut the facts exist in 

 Italy, in many islands of Africa and the Indian archi- 

 pelago, in the West Indian islands, and in the Coral 

 islands of the Pacific ocean. The power is that of 

 volcanoes, of different periods ; and, for the elevated 

 substances, I must refer to preceding chapters. 



From this point, there can no longer beany assign- 

 ment of dates, since each class of alluvia is in daily 

 progress, somewhere; as all have been, from the com- 

 mencement. I therefore muster them as appears most 

 convenient. Lakes have been drained or filled, at all 

 periods, as the same events are still occurring. Their 

 strata, solid or loose, and sometimes containing organic- 

 bodies, have been confounded with the proper tertiary 

 strata: as I observed before. Properly, they rank here, 

 in a just Theory. Yet let me remark, that such events 

 ought to have occurred in every anterior condition of 

 the globe, as it certainly did at the formation of coal: 

 whence perhaps have arisen some appearances in the 

 antient strata, still requiring explanation, and also, 

 some further examination. I might have said, that 

 geologists have too much forgotten, that every antient 

 state of the Earth must have resembled the present, 

 as to its surface and the changes to which this was sub- 

 ject; but they have not even imagined these former 

 Conditions ; with but a limited exception. What such 

 considerations, and many more which have preceded, 

 will hereafter effect for geological science, remains to be 

 seen: it will never be known by me; but it is some 

 satisfaction to find that there is abundant work for the 

 future, as I have here endeavoured to conjecture what 

 it is; guided by the only beacon that an imperfect 

 science can afford. If Geology is sleeping, let it rouse 

 itself: we are ever hearing a great deal that is not 

 true, very much that leads to nothing, and far more 



