SLATES. 319 



You have witnessed the phenomena of crystallisation, 

 and have had placed before you the facts which are 

 found associated with the cleavage of slate rocks. Such 

 facts, as expressed by Helmholtz, are so many tele- 

 scopes to our spiritual vision, by which we can see 

 backward through the night of antiquity, and discern 

 the forces which have been in operation upon the 

 earth's surface 



Ere the lion roared, 



Or the eagle soared. 



From evidence of the most independent and trust- 

 worthy character, we come to the conclusion that these 

 slaty masses have been subjected to enormous pressure, 

 and by the sure method of experiment we have shown 

 and this is the only really new point which has been 

 brought before you how the pressure is sufficient to 

 produce the cleavage. Expanding our field of view, 

 we find the self-same law, whose footsteps we trace 

 amid the crags of Wales and Cumberland, extending 

 into the domain of the pastrycook and ironfounder; 

 nay, a wheel cannot roll over the half-dried mud of our 

 streets without revealing to us more or less of the fea- 

 tures of this law. Let me say, in conclusion, that the 

 spirit in which this problem has been attacked by 

 geologists, indicates the dawning of a new day for their 

 science. The great intellects who have laboured at 

 geology, and who have raised it to its present pitch of 

 grandeur, were compelled to deal with the subject in 

 mass; they had no time to look after details. But the 

 desire for more exact knowledge is increasing; facts are 

 flowing in which, while they leave untouched the in- 

 trinsic wonders of geology, are gradually supplanting 

 by solid truths the uncertain speculations which beset 

 the subject in its infancy. Geologists now aim to imi- 

 tate, as far as possible, the conditions of nature, and to 



