VOLCANIC SERIES OF ST. DAVIDS. 253 



older tuff and more sedimentary-looking material in the upper beds 

 of the Pebidian series. 



Turning to the conglomerate, it appears that the fragments of 

 Pebidian aspect diifer from those contained as inclusions in the 

 Pebidian tuffs chieflj' in their larger size. I paid a good deal of 

 attention to the Pebidian pebbles on the modern beach in the 

 neighbourhood of cliffs of this age, and was forcibly impressed bj' 

 the fact that no pebbles of similar form, structure, and aspect 

 occurred, so far as 1 was able to observe, in the conglomerate. 



I have no desire to underestimate the value of the evidence of 

 these abnormal inclusions in the conglomerate. I hold no brief for 

 either party in this controversy. My sole desire was to reach, if I 

 might, the truth concerning the relation of Pebidian to Cambrian. 

 The evidence of these fragments seemed at first to contradict the 

 stratigraphical evidence. But further study tended to show that 

 this contradiction might be apparent only, and that the Pebidian 

 fragments might well be derived from inclusions in the tuffs washed 

 out of these deposits by the current which bore onward the more 

 numerous foreign materials of the conglomerate. 



g. Summary of the Evidence. — The evidence as to the relation of 

 Pebidian to Cambrian at St. Davids is, in my opinion, not such as 

 to enable one to lay down the law with ease and precision. It is 

 such that two geologists who were at one concerning the facts 

 observed might nevertheless differ as to the exact position and value 

 in the stratigraphical scheme to be assigned to the Pebidian series. 

 On the one hand we have in the Cambrian conglomerate an 

 apparently satisfactory base to a natural system of stratified de- 

 posits ; we have in that deposit fragments derived from the under- 

 lying strata ; we have evidence of some transgression of the con- 

 glomerate across the edges of the subjacent beds. On the other 

 hand we have a marked parallelism of strike and a general uniformity 

 of dip in the beds of both Pebidian and Cambrian ; the included 

 Pebidian fragments are such as might have been washed out of 

 Pebidian tuffs ; and the transgression across the subjacent beds is 

 nowhere more than one has a right to expect where a current- 

 borne material, such as a coarse conglomerate, follows upon soft 

 beds of recent formation. It is remarkable that both to the south 

 of the St. David's axis and to the north, where in each case the 

 parallelism of strike is so marked that I could nowhere make 7f of 

 difference, we have evidence of the incoming of sedimentary con- 

 ditions in the Pebidian similar to those which are indicated by the 

 Cambrian beds that succeed the conglomerate. And it is note- 

 worthy that in those overlying Cambrians we have evidence of the 

 continuance of volcanic conditions which characterize the Pebidian. 

 Moreover, at Carn-ar-wig we seem to have satisfactory evidence of 

 the interdigitation of Cambrian conglomerate and Pebidian ashes. 

 Taking all the facts into consideration, I am led to the conclusion 

 that the break between the two systems was not of any great 

 magnitude, and that the change of conditions emphasized by the 

 conglomerate was one which followed, after no great lapse of lime, 



