59 



These analyses are confirmatory of the main points of the views 

 already stated, and seem clearly to establish the new and remarkable 

 fact, that by the igneous action in these instances the magnesia 

 has been driven off from the limestone. The unaltered rock is a 

 dolomite containing nearly 70 per cent, of carbonate of lime, and 

 nearly 20 per cent, of carbonate of magnesia ; while the altered rock 

 contains but from 1 to 2 per cent, of the latter ingredient. To 

 what cause are we to assign the changes that have taken place? 

 Has the magnesia been sublimed by heat ? or has it been withdrawn 

 by the solvent power of free carbonic acid ? On the nature of these 

 and the other chemical changes that have been induced, it is diffi- 

 cult to express an opinion ; and from such limited premises it would 

 be unphilosophical to draw any general conclusions. The subject is 

 one, however, of great interest both to the geologist and chemist, 

 as the facts are directly opposed to the received views ; * and as no 

 instance of similar changes on dolomitic rocks has, so far as we are 

 aware, ever been put on record. 



40. A remarkable dike intersects the sandstone between Ascog 

 and Kerrycroy, well worthy of attention on account of the striking 

 illustration it affords of the mode of cooling of basaltic rocks from 

 igneous fusion. It runs parallel to the shore for some distance, and 

 then retires from it towards the S.W., and striking the inland cliff 



Side view of whin dike between Ascog and Kerry eroy. 



already mentioned, whose direction is here the same as that of the 

 dike, it forms the perpendicular face of the cliff in front of the sand- 

 stone, rising like a wall to a height of twenty or thirty feet. The direc- 



* For the latest and best account of the views of geologists on this subject see the 

 well known work of Dr. Daubeny on Volcanoes, new edit. ; also an admirable resume in 

 the anniversary address of Prof. Oldham in the Journal of the Dublin Geological Society r , 

 1R19. 



