Geological Society of London. 331 



rocks of St. David's is the occurrence of four distinct species of tlie 

 genus Paradoxides ; and this is in strong contrast with the entire 

 absence of the genus Olenus. On a comparison of the palaeontology 

 of the St. David's rocks with those of the Continent of Europe and of 

 America, which seem to occupy nearly the same horizon, we have 

 like features to a very great extent presenting themselves. 



With reference to the distribution in time of some of the earlier 

 genera of Trilobites, it would appear that the genus Olenus is repre- 

 sented in Britain and Europe by twenty -two species, confined to the 

 Lingula-flags and Tremadoc rocks, and not occurring so low as the 

 Menevian group. The absence of this genus from the Menevian 

 group, and its occurrence throughout the whole of the Lingula-flags, 

 and in the Tremadoc rocks, along with the fact that so far as pre- 

 sent observations go, no species of Paradoxides ranges higher than 

 the Menevian group, have afibrded good palasontological grounds for 

 placing the line of demarcation between Upper and Lower Cambrian 

 at this spot, and for including the Menevian group in the Lower 

 Cambrian, to the bulk of which it is intimately united palseonto- 

 logically. 



Discussion. — Mr. Hughes bore testimony to the admirable work done by Mr. 

 Hicks, who had, almost unaided, worked out the geology of that district. Allowing 

 that many subdivisions and new specific names had with great advantage been intro- 

 duced into petrology, he defended the Survey nomenclature by reference to the then 

 received definition of Syenite and Greenstone, terms still perfectly understood and 

 applicable to the main mass of the rocks in question, though possibly subsequent closer 

 examination and new sections may have rendered some modification of the boundary 

 lines desirable. He was prepared to allow the metamorphic origin of all rocks of the 

 classes under consideration, but did not think there was suflScient evidence to show 

 that the divisional planes in the Syenite and Greenstone of St. David's were due to 

 original stratification, but might correspond rather to the great joints of most 

 granites. Mr. Hughes pointed out that the conglomerate contained fragments of the 

 hornstone and quartz of this older series, which he considered was probably part of 

 an old ridge or shoal, possibly of Laurentian, but certainly of pre-Cambrian age, and 

 thought that there were slight differences in the lithological character of the beds on 

 either side, such as might be explained on this supposition. H e agreed with Prof. 

 Eamsay in thinking that there was evidence of the proximity of land in early 

 Cambrian times, but was not prepared to refer these red rocks to inland seas or lakes 

 as opposed to open' sea, the whole seemed rather the deposit of an open sea encrpach- 

 ing during submergence. ' He did not attach very much importance to the restriction 

 of genera to limited horizons in these older rocks of St. David's. For, as it was re- 

 served for Mr. Hicks to discover these fossils after so many other observers had 

 examined the district, he anticipated that further researches must certainly result in 

 finding links which vrill connect together more closely beds, the stratigraphical rela- 

 tions of which seem to indicate so clearly an unbroken though varying series. 



Mr. Gwyn Jefi'reys had been struck by the intercalation of non-fossiliferous beds 

 from time to time among the fossiliferous beds described in the paper. This was the 

 case in beds now in course of formation, and appeared to arise from the great deposits 

 of mud brought down by rivers and redeposited in certain positions in the sea-bed. 

 That this was the case had been proved by recent dredging operations both in the 

 Atlantic, oflF Spain, and in the Mediterranean. 



Mr. Boyd Dawkins called attention to the gap which had been filled by the dis- 

 coveries recorded in the paper, inasmuch as the Molluscan, Annelid, and Crustacean 

 forms were now carried back far into the Cambrian period, and yet without any trace 

 of their convergence, so that the origin of life might be as far removed from that 

 period as was the Cambrian ft-om the present time. The difl'erence in the colours of 

 the rocks he was inclined to refer to the diff'erent degrees of oxidization of the iron 

 they contained, which might supervene in a comparatively short time. 



