Il6 THE OLDER ROCKS OF ST. DAVIDS. 



lines of least resistance — in other words — the Dimetian was 

 consolidated, and had assumed its crystalline aspect and present 

 system of joints before the basic rock was intruded. 



Near Forth Lisky, Dr. Hicks also pointed out to us the 

 limestones described by him {I. c. p. 232) last year : he showed us 

 that most of them were inclined in the same direction as the 

 crystalline schists in which they were intercalated. But one at 

 any rate at one place dipped in an opposite direction, as if there 

 had been an anticlinal. We coald discover however no proof of 

 an anticlinal in the crystalline rock, and we are disposed to seek 

 for another explanation of the bands of limestone. We notice 

 that the texture of this limestone is coarsely crystalline, and the 

 band contains much serpentine in blotches and streaks. We 

 suggest that it is not likely that these thin bands with crystals of 

 dolomite, calcite, &c., as described in Mr. Huddleston*s analysis, 

 could be of anything but of secondary origin in a metamorphic 

 series enclosed between walls of such an acidic rock as in the 

 Dimetian here. The thinness of the bands, one to three feet, 

 seems to render it possible that their orign is due to the 

 decomposition caused by water filtering down joints, removing 

 alkahne silicates and depositing carbonates of lime and magnesia j 

 the presence of serpentine too may be held to strengthen this 

 hypothesis. The percolating waters would have taken the 

 direction of the main divisional planes, which are here the ancient 

 bedding as a rule, while in the one exceptional case they may have 

 followed one of the other system of joints, and thus a calcareous 

 band have been formed dipping apparently in an opposite 

 direction. This explanation arrived at in the field seems to agree 

 with the described chemical and microscopical analyses of the rock 

 by Messrs. Huddleston and Davies (I. c. p. 234, note). 



A few words on the Dimetian rock at Forth Lisky, the 

 microscopic structure of which was described by Mr. Davies 

 {ibid. p. 231, note). It is said in places to contain very Httle 

 felspar. No doubt this is true, but such a state is perhaps 



