The Rev. Prof. Blake — Base of the Sedimentary Series. 311 



With regard then to the St. Davids district, the net result of past 

 researches amounts to this. There are below the Cambrian con- 

 glomerates a series of bedded rocks, partly of volcanic and partly of 

 sedimentary origin. Associated with these there is a mass of granite 

 which is bounded in many places by quartz porphyrites. The granite 

 is not actually seen to intrude into anything, but the quartz por- 

 phyries may be either its apophyses, or a later eruption which is 

 more or less intrusive into both it and the volcanic ashes. The 

 whole of this group is distinct in character from the Cambrian rocks 

 which succeed (with insignificant exceptions), and there is an 

 interval of time between them ; but of what amount, or of what 

 importance, this interval may be, is at present an open question, 

 probably not to be settled without introducing considerations derived 

 from other areas. All this does not seem to be more than might 

 have been made out by a good geologist working for a fortnight 

 on the ground, but the labour that has been spent will not have 

 been thrown away, if we are taught caution in the use of theories 

 of metamorphism from the utter failui % e of even geologists of credit 

 to make out bedding in massive crystalline rocks which we might 

 as soon expect to discover as the original stratification of an earthy 

 iron ore in a bar of pig iron made from it. 



To the series thus determined — whether it be a subdivision of the 

 Cambrian or a portion of an anterior s_ystem of rocks — the "local 

 name " of Pebidiau rightly belongs. The use of the same word 

 for any minor gi'oup in other areas depends on a more accurate 

 correlation than has yet, been accomplished. 



2. Anglesey. — In his earliest classificatory paper, Prof. Sedgwick 

 placed the older rocks of this island in his Lower Cambrian group, 

 making what is now known as Cambrian proper his Middle Cam- 

 brian, while our Ordovician rocks were his- Upper Cambrian. In 

 later writings, however, he excluded the Anglesey rocks from the 

 Cambrian, which he then made to commence with the " Llanberis 

 slates." In deference, however, as it seems, to the views of the 

 Geological Survey, he left it an open question whether the Anglesey 

 rocks might not be altered representatives of some part of his Cambrian 

 system, though it is obvious that he did not of his own accord con- 

 sider them as such. With regard to the opinion of Prof. Ramsay 

 that all the older rocks of Anglesey were metamoi'phosed represen- 

 tatives of the Cambrian, we need not imagine that he supposed they 

 were the very same beds as are seen on the mainland continued into 

 the island in an altered state, but that he found no line of demarc- 

 ation between them, and no necessity to consider them of a different 

 system, but rather as a downward extension of the Cambrians which 

 were here entirely metamorphosed. Such appears also to have been 

 Sedgwick's original opinion when he called them " Lower Cambrian." 

 And such for many years, in deference to the deservedly respected 

 teaching of Prof. Ramsay, they were held to be. As soon, however, 

 as attention began to '.be turned to possible Precambrian rocks, 

 Anglesey was naturally thought of. Accordingly, in 1878, Dr. 

 Hicks examined the junction of the granite at Llanfaelog with the 



