62 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



briau rocks seem to have no equivalents in North Wales, unless they 

 represent in time the Llanberris, Harlech, and Bangor sandstones, 

 grits, and flags, which, however, have as yet yielded no trace of organic 

 remains. Again, very few species are common to these grey, red, and 

 purple sandstones and the succeeding well-developed Menevian 

 group, which has yielded nearly fifty species* ; yet in the Harlech, 

 Barmouth, and Dolgelly areas the Menevians immediately succeed, 

 are conformable to the underlying barren unfossiliferous grits, and 

 exhibit the first traces in North "Wales of a definite and defi- 

 nable fauna. In other words, the representatives of the Harlech 

 and Llanberris beds in the St. -David's promontory contain a 

 well-marked fauna, highly characterized by the Crustacea (7 

 genera and 14 species) and by the still more important fact 

 that no species occurring in the Longmynd and Harlech rocks of 

 St. David's are known in North Wales. It is only in the succeeding 

 Menevian (Lowest Lingula-flags) that there is a well-marked com- 

 munity. Of the 12 Pembrokeshire species (9 of which are 

 Trilobita, viz. Agnostus cambrensis, Conocoryplie bufo, 0. Lyellii, 

 O. solvensis, Microdiscus sculptus, Paradoxides aurora, P. HicJcsii, 

 P. HarJcnessii, and Plutonia JSedgivicld.i) not one is known out of 

 the area ; whereas of the 28 Menevian species known in the St.- 

 David's area, 12 are common to it and North Wales and 5 are con- 

 fined to North Wales, viz. Agnostus reticulatus, Ang., Anopolenus 

 impar, Hicks, Conocoryplie coronata, Barr., C. Homfrayi, Salt., 

 and Erinnys venulosa, Salt. ; 7 are common to both areas, and 

 16 peculiar to the Menevian promontory. These will be referred 

 to under the Menevian group. 



This non-occurrence of fossil remains other than Annelide-burrows 

 (Chondrites and Cruziana) in the Cambrian of the Geological Sur- 

 vey has much significance when they are compared with groups of 

 rocks equivalent in time, and not far removed geographically, meta- 

 morphism not having affected their original condition so as to have 

 obliterated all traces of life. The sequence in both areas (North and 

 South Wales) is the same, as proved or determined by the position 

 of the Menevian beds, which in South Wales have a fossiliferous 

 base in grey, red, and purple sandstones, these, again, resting upon 

 a Pre-Cambrian foundation of highly metamorphosed rocks, divisible 

 into three systems or formations, which Dr. Hicks has denominated 

 Dimetian, Arvonian, and Pebidian, all having different strikes or 

 bearings. We must remember that the Menevian beds of North 

 Wales rest (so far as is at present known) on the unfossiliferous 

 Bangor, Llanberris, and Harlech grits throughout their known ap- 

 pearance and range. 



Lowee Cambrian Rocks. 



The fossils which occur in the lowest known part of the Harlech 

 and Bangor group at St. David's are Lingulella ferruginea, Salt., L. 



* The Middle Cambrian or Lower Lingula-flags of Sedgwick, the Lingula- 

 flags of authors, and the Upper Cambrian of Lyell and Salter ; the Menevian 

 group of Salter and Hicks. 



