238 H. HICKS ON TIIE rEE-CAMBHIAN ROCKS OF ST. DAVIDS. 



coast sections ; and frequently the line can be followed right across 

 the island from side to side, as the surface is almost entirely 

 barren. The fault on the east side of the hill has a downthrow 

 of at least 14,000 feet, as the Arenig beds found here are the 

 highest in stratigraphical position in that group. The fault which 

 meets it at the N.E. end has also a dowmthrow of nearly equal 

 extent, since the Arenig beds are again brought down against the 

 very lowest beds of the Cambrian. 



About eight miles to the east of St. David's, on the coast near 

 Newgate Sands, there is an oblong patch coloured as granite in the 

 Survey map. This, again, is made up of these Pebidian beds, in 

 somewhat the same state of alteration as in the other places men- 

 tioned ; and the Cambrian conglomerates again rest upon them un- 

 conformably. It is more than probable that there are other expo- 

 sures of these rocks to the east of the areas already described, a?rd 

 that portions at least of the so-called granites of Brawdy and Hays- 

 castle, and of the felstones to the north of Llanrithan, will prove to 

 be made up of these metamorphosed Pebidian beds. My researches 

 in these neighbourhoods hitherto, however, have not been sufficient 

 to enable me to speak decidedly on this point, though I have recog- 

 nized in these masses rocks of like character to those at St. David's, 

 and have already obtained facts which tend to show that the unaltered 

 Cambrian beds overlie these also unconformably. 



The Pebidian rocks, in consequence of having a strike frequently 

 nearly identical with that of the overlying Cambrians, have been 

 included with the latter in some of my former papers, though even 

 in these I always pointed out that the}^ formed a distinct group in 

 that formation. Finding on further examination, however, that the 

 two groups are everywhere unconformable to one another, that the 

 rocks in the one are throughout always highly metamorphosed, 

 and in the other unaltered, and, what is still more important, that 

 the true Cambrian conglomerates undoubtedly contain masses of the 

 underlying rocks in their altered state, very frequently as pebbles, I 

 have thought it necessary to distinguish them from one another by a 

 stronger line, and hence have in this paper classed these lower beds 

 under the new name of Pebidian. It is certain that some of the 

 boundaries of these rocks will yet have to be enlarged, and that 

 most of the patches coloured as altered Cambrian will prove to be 

 made up of these rocks. In this paper my endeavour has chiefly 

 been to point out spots where the unconformity between them and 

 the Cambrians above, or the Dimetians below, is well marked, 

 rather than to give the superficial areas. 



Conclusions. 



Prom the foregoing remarks it will be seen that nearly all the 

 large so-called intrusive masses associated w T ith the lower Cambrian 

 rocks in the promontory of St. David's are only highly meta- 

 morphosed sedimentary rocks — and that, instead of being intruded 



