The Rev. Prof. Blake — Base of the Sedimentary Series. 309 



altered representatives of ordinary sediments, in Dr. Hicks's, the 

 crystalline masses were considered as stratified rocks whose bedding 

 had been almost or entirely obliterated. In his original paper 

 (1877) he stated that the " Dimetian series, near St. Davids, are 

 chiefly quartz-schists, chloritic schists, indurated shales," while at 

 Poithlisky "the quartzose beds are less altered," and "we find 

 massive beds of calcareous shale and chloritic schists, and associated 

 with them also dolomitic limestone beds several feet in thickness." 

 The series was stated to have a constant strike to the south-east, and 

 to be 15,000 feet at least in thickness— a very definite description. 

 The " Pebidian " had a strike nearly at right angles to this, and 

 " consist chiefly of indurated shales, often porcellanitic in character," 

 while " the lower beds, resting immediately on the Dimetian axis, 

 are hai'd compact conglomerates chiefly composed of masses of quartz 

 and altered shale, or such masses as might have been derived from 

 the underlying rocks," and on the west side the appearance of 

 the rocks is much like that at St. Davids, but there is a larger 

 proportion of greenish and purplish schists alternating with the 

 compact porcellanite shales, " so that there is every probability we 

 have a repetition of the whole series," and "on the S.W. of Ramsey 

 Island the beds are compact porcellanites like those near St. Davids, 

 and the bedding is also easily traced." 



Such was the original description — in which it will be noticed 

 that there was not a single word about granitoid rocks, quartz 

 felsites (except as a dyke), agglomerates, or volcanic ashes. 



In the following year, however (1878), he had gone over the 

 ground again in company with Mr. Hudleston and Prof. Hughes, 

 and it is not too much to say that in all essential features, the 

 lithological description of the rocks were entirely altered, so that it 

 is not difficult to say who, rediscovered, so to speak, the volcanic 

 series. Now we hear that the Dimetian consists of " quartz porphyries, 

 fine-grained quartz-felsites, ashy shale-like rocks (which turn out 

 to be altered basalts), compact granitic-looking rock, quartziferous 

 breccias, granitoid quartz schists somewhat chloritic, schistose bands 

 which are also basalts,. and crystalline limestone bands." Thus the 

 quartz schists turn out to be for the most part granitic-looking rocks 

 and quartz porphyries, the indurated shales are basalt dykes, and 

 the dolomite beds several feet in thickness are calcareous infiltrations 

 along joints. It will be noted also that the quartz porpyhries and 

 felsites are placed at the base of the series. It is still maintained, 

 however, that the whole is bedded. Passing to the Pebidian, we 

 now hear of agglomerates at the base, felspathic breccias, indurated 

 ashes, volcanic tuffs, conglomeratic and ashy beds, a thick band of 

 felstone, probably a contemporaneous lava, and bright green ashes, 

 in addition to the porcellanites, schists, and conglomerates, which 

 alone made up the series before. Moreover, the beds on the west 

 are not now repetitions of those on the east, but higher in the 

 series, while the mass in Ramsey Island, instead of being a bedded 

 porcellanite, consists of felstone, felstone porphyry, hornstone, and 

 felspathic breccias. It is scarcely possible to imagine a more complete 



