22 Br. Henry Hicks — Olenellus Zone in Wales. 



and that the horizon of the fauna is yery near the base of the series. 

 As this fauna is separated by about 1000 feet of red and purple 

 sandstones and slates from the next overlying fauna {Plutonia 

 Sedgwiclcii and Conocoryphe Lyellii zone), it is quite possible that 

 other zones, containing different species, may occur between, for in 

 the higher beds containing Paradoxides each important zone is 

 characterized by a new species. In the Cambrian succession at St. 

 David's the most marked changes in the sediments occur almost 

 immediately below the Plutonia beds, and at the top of the Menevian, 

 but the greatest palgeontological break is undoubtedlj' at the close of 

 the Menevian. This tempted me in former papers to divide the 

 Cambrian at St. David's into an Upper and a Lower division only, 

 but as, at present, there seems to be a desire to make a threefold 

 division, there can be uo serious objection to restricting the terms 

 Lower Cambrian to the Caerfai Group (Olenellus fauna). Middle 

 Cambrian to the Solva and Menevian Groups [Paradoxides fauna) 

 and Upper Cambrian to the Maentwrog, Ffestiniog, Dolgelly and 

 TremadoG Groups. I may here mention that the sandstones at the 

 top of the Menevian, which yielded Ortliis Hicksii and other Brachio- 

 pods, are now known to contain a Paradoxides, probably a new 

 species, and a new species of Conocoryphe (which I hope to describe 

 shortly). This somewhat extends the range upwards of Paradoxides, 

 but the genus is still confined within the limit of the Menevian 

 Group. 



North Wales. 



After referring to the fossils found in the Lower Cambrian rocks 

 of St. David's, Mr. Walcott says (p. 580) : "These, with the species 

 from North Wales, described by Dr. Henry Woodward ^ as Cono- 

 coryphe viola, do not prove the presence of the Olenellus zone; but 

 the weight of stratigraphic evidence is so strongly in favour of 

 including them in its fauna that 1 shall do so. In the summer of 

 1888 I visited the locality of Conocoryphe viola, and found fragments 

 of it associated with a species of Hyolithes." Mr. Walcott's visit 

 was made during the excursion of the International Geological 

 Congress, which I conducted to the Penrhyn Slate Quarries, in 1888. 

 The position of this fossil is given in the " Explication des 

 Excursions," p. 38, as near the horizon of the Plutonia and Cono- 

 coryphe Lyellii zone at St. David's ; but it is quite possible that it 

 might be somewhat lower than that horizon, though evidently higher 

 than the Lingnlella primava zone. Most of the red and purple slates 

 occur below the C. viola zone, and there are evidences of fossils in 

 these beds. The succession in the Cambrian rocks at Penrhyn, 

 Llanberis and in the Harlech Mountains, so nearly resembles that 

 at St. David's that it has been possible to indicate the position in 

 those areas of all the main zones found at St. David's, and at present 

 it only remains for them to be worked out. 



The following section contains the chief fossiliferous zones which 

 are now known to occur in the Cambrian rocks of Wales, and by 

 its side I place a section which was given for Wales in my paper 

 1 Quart. Journ. Geol. Soc. vol. xliv. p. 74. 



