144 TOWN GEOLOGY. [TI. 



between rocks far newer than it, on one side to a 

 height of eight hundred, on the other to a height of 

 eighteen hundred feet half the present height of 

 Snowdon, Nay, the very slate beds of Snowdonia 

 have not forced their way up from under the mountain 

 without long and fearful struggles. They are set in 

 places upright on end, then horizontal again, then 

 sunk in an opposite direction, then curled like sea- 

 waves, then set nearly upright once more, and faulted 

 through and through, six times, I believe, in the 

 distance of a mile or two ; they carry here and there 

 on their backs patches of newer beds, the rest of 

 which has long vanished; and in their rise they have 

 hurled back to the eastward, and set upright, what is 

 now the whole western flank of Snowdon, a mass of 

 rock which was then several times as thick as it is 

 now. 



The force which thus tortured them was probably 

 exerted by the great mass of volcanic Quartz- 

 porphyry, which rises from under them to the north- 

 west, crossing the end of the lower lake of theLlanberris; 

 and indeed the shifts and convulsions which have taken 

 place between them and the Menai Straits are so vast 

 that they can only be estimated by looking at them on 

 the section which may be found at the end of Professor 

 Ramsay's "Geological Survey of North Wales." But 

 anyone who will study that section, and use (as with 

 the map) a little imagination and common sense, will 

 see that between the heat of that Porphyry, which 

 must have been poured out as a fluid mass as hot, 

 probably, as melted iron, and the pressure of it below, 

 and of the Silurian beds above, the Cambrian mud- 

 strata of Llanberris and Penrhyn quarries must have 



