THE CHEESE^VRI^^G, CORNWALL, AND ITS TEACHINGS. 153 



under the ocean at any recent period at all, and they refer all the 

 escaT-pments and table-lands and plains to the agency of running 

 water. 



Lord Avebury, in his volume to which I have referred, and 

 strongly recommend every one to read, goes very near holding the 

 same opinions as myself ; but he does not go quite so far, I think. 

 He puts, perhaps, more stress on running water in forming escarp- 

 ments than I am disposed to do ; but at any rate we are very nearly 

 in harmony on that subject. 



Dr. Walker referred to the sea-stacks rising from the sea. Of 

 course as we approach the coast of the British Isles from the 

 outer ocean we can often, over the area formed by the Cor- 

 tinental Platform, see these stacks. But sea-stacks and islands 

 are really harder portions of the original strata which the sea had 

 not had time to wash away. Ultimately, I suppose, the sea will 

 level down most of the sea islands and sea-stacks that bound our 

 coast ; but it must be a matter of time. 



Mr. Rouse and Colonel Alves referred to the existence of water in 

 granite. I have examined under the microscope a good many 

 sections of granite, principally from Ireland, and in almost all cases 

 the silex or quartz of the granite was found to contain minute cavities 

 filled with liquid. They are exceedingly small, and it is only in the 

 quartz that these cavities occur, not in the felspar or in the mica. 

 Tlie explanation of this seems to be that the quartz is generally found 

 to be non-crystalline in form. There is a crystalline structure (as it 

 polarizes), but the form of crystal is not developed as in the case of 

 mica and felspar ; and the explanation is that the quartz was the last 

 of the three minerals to consolidate. It had been kept in a pasty 

 condition by the presence of water, and, no doubt, water containing 

 carbonic acid, which must have been in a state of highly super- 

 heated steam at the time the granite was in the course of con- 

 solidation. Thus the crystals of mica and felspar had time to form 

 iind were embedded in this paste of quartz (with fluid cavities) which 

 ultimately, as time went on, became solid. 



That is the explanation I venture to offer for the remarkable 

 phenomenon of the appearance of acid water in granite. 



Dr. Jack put a question about the Logan Rock near Land's End. 

 I have not myself been there, but the Logan Rock which is described 

 by Wilkie Collins is a large monolith, so nicely balanced on its floor 



