358 



THE GEOLOGIST. 



was complete. He did not consider that the moulded ornaments manu- 

 factured from fused basalt had a tendency to decay or become decomposed 

 by exposure to the atmosphere. He believed they would be found very 

 durable when used in buildings. Mr. Atkinson asked if in the section of 

 a bed of lava, for instance of the depth of 15 or 20 feet (or of the height 

 of this room), the lowest portion which had sustained the greatest pressure, 

 or the part which had been longest in cooling, ever assumed a crystalline 

 structure similar to granite ? Signer Berruti replied that the material was 

 more compact, and showed traces of crystalline structure, but the crystal- 

 lization was very different from that of granite. 



Mr. Hull said if there was one question more than another we might 

 consider absolutely settled in geology — though some geologists deny that 

 anything at all has been settled — it is that these different varieties of trap, 

 passing from greenstone and basalt into obsidian, are the result of differ- 

 ences in the rate of cooling under pressure. But when we come to the 

 question with regard to granite, there, at once, we perceive a distinction.. 

 There is something very different and distinct between granite and lavas 

 and other trap rocks. The great question is, why there should be such a 

 distinction. We all know that granite is a highly crystalline rock, and the 

 reason that we failed in making any approach towards forming granite by 

 artificial processes of cooling is that we are attempting to do, on a small 

 scale, what nature does on an enormous one, and with overwhelming forces 

 and length of time, in her own laboratory. We can make no approach to 

 the enormous pressure that nature has been able to employ during the 

 cooling of the granite ; nor can we lengthen out the time which granite has 

 taken to cool within the bowels of the earth. It is now known by clear 

 observations, some of which have been made in Dartmoor and other parts, 

 that granite is nothing else but the melted stratified rock, passing some- 

 times into slate rocks ; and so gradual is this passage, that it is sometimes 

 difficult to say where one form of rock commences and the other ends. 

 This shows us that granite is the result of metamorphism of the stratified 

 rock at an enormous depth, in all probability when the rock was overlaid 

 by many thousands of feet of strata, which have been since removed. 

 Thus, in Devonshire, in the case of the granite of Dartmoor, the bosses of 

 granite which appear there lie in the very strike of the beds, and occupy 

 the place of certain members of the slate-rocks of that district. ^Nothing 

 could better prove that granite is a highly-metamorphosed form of strati- 

 fied rocks. The President, Mr. Dickinson, remarked that Mr. Hull has 

 told us about the numerous points which have been settled in geology, and 

 that if there is any one which is settled it is this one. He had now been a 

 long time engaged in pursuits which have given him very great opportunities 

 for "observing the geological structure of the earth. In the course of those 

 opportunities be had examined rocks similar to those exhibited to-day, both 

 in Northumberland, Cumberland, Durham, Westmoreland, Cornwall, De- 

 vonshire, JN T orth Wales, and in inaivy portions of Scotland, at the Giant's 

 Causeway and Fair Head, in Ireland, also in the south of France, in Saxony, 

 and in the Hartz Mountains, and other places ; and as the result of his 

 observations he was prepared to admit that the fusing of these rocks does 

 give results similar to those that are occasionally found in nature ; but with 

 regard to the origin he was disposed to think geologists have settled far 

 too much, and will have to unsettle a good deal of what they have decided 

 upon. The way in which many of the trap rocks are found blended with 

 the slates, etc.. was to his mind a point of difficulty to be got over before 

 \\ e can recognise them as being formed by igneous action. The way in 



