274 A. GEI1IIE ON THE SUPPOSED 



calations, though the occasional occurrence of micaceous and 

 chloritic schists is referred to. I have been unable to determine 

 what portions of the mass of rock at St. David's could have been 

 regarded by him as stratified or foliated intercalations of any kind. I 

 believe him to have been deceived sometimes by the greenish decayed 

 material filling up the partially opened joints, sometimes by the 

 diabase dykes and veins. He appears also to have included in his 

 " Dimetian " group portions of the undoubtedly bedded rocks (quartz- 

 schists, quartzites, shales, &c.) which flank the massive rock of the 

 ridge, as will be shown in the subsequent description of the coast- 

 section at Porth-lisky. I repeat in the most emphatic manner 

 that, after an exhaustive search over the whole ridge in question, 

 neither Mr. Peach nor I could find the slightest trace of any shale, 

 schist, quartzite, gneiss, or other stratified rock, bedded with that 

 composing the ridge between Bryn-y-garn and the headlands south 

 of Porth-lisky — nor of bedding or definite structure of any kind, 

 save the joints universally present in similar massive rocks. "We 

 cannot even conjecture on what grounds the assertion has been so 

 often made that the central part of the ridge is bedded, and that 

 its bedding has an invariable strike from N.W. to S.E. We could 

 see absolutely nothing in the rock to afford any basis for such a 

 statement *. 



Did no other than petrographical characters exist to guide us, 

 these are so clear in their concurrent testimony that there could be 

 no doubt as to the propriety of placing the rock in question among 

 the granites. It has the usual typical features of a granite, and 

 none of those of a schistose rock. 



But further evidence is abundantly available. That this rock is 

 not only a granite but one which has been erupted through the 

 Cambrian strata, and must therefore be younger than they, is 

 admirably demonstrated by the way in which rt behaves to the 

 rocks that surround it. A field-geologist naturally turns at once to 

 the line of junction between two rock-masses to ascertain their 

 mutual relations. Unfortunately, in most cases such a line is so 

 much obscured by superficial deposits that the actual contact of the 

 rocks can, at the best, be seen only to a limited extent and in few 

 places. At St. David's, however, the coast-section and the trans- 

 verse valley cut by the river Allan permit the actual junction of the 

 granite with the surrounding rocks to be seen at several localities 

 and on both sides. I have searched in vain among the published 

 papers for any account of these localities. It is difficult to believe 

 that they can have been actually seen by any one who could after- 

 wards maintain the rock to be Pre-Cambrian in age and meta- 

 morphic in origin f. They show the granite to be unmistakably 



* On the occasion of my second visit to St. David's I again sought, with 

 Mr. Topley, for any trace of foliation or bedding in the crystalline rock of the 

 ridge, but equally without success. 



t It appears that Dr. Hicks started with the idea expressed on the Geological 

 Survey map that the crystalline rock of the St. David's ridge is intrusive. He 

 afterwards wrote that " on further examination it seemed clear that the syenite 



