494 Belt— 071 the "■ Lhigula Flags!' 



labours of Mr. Hicks, The strata containing these trilobites have 

 been separated from the Lingula Flags by Mr. Salter, under the 

 name of the Menevian Group. The recent discovery by Mr. Hicks 

 of new forms of Pm-adoxides in the purple slates, inter-stratified 

 with the Harlech grits, will probably lead to the classification of 

 the Paradoxides beds as Lower Cambrian. The Menevian Group 

 will then form the top beds of the lower instead of the bottom beds 

 of the upper formation and the Lower Cambrian will have a 

 well-defined palasontological limit upwards. Whilst linked to the 

 upper series by such general and far ranging forms as Conocory])he 

 and Agnostus, it will be distinctly marked off by Paradoxides and 

 other genera that do not transgress the upper boundary of the 

 Menevian beds. 



The Lingula Flags above the Menevian Group have been di^^ided 

 by Mr. Salter into the Lower, Middle, and Upper Lingula. In a 

 paper by Mr. Plant, an abstract of which appears in the Quarterly 

 Journal of the Geological Society for November, 1866, the same 

 classification is adopted. Messrs. Salter and Hicks, in the Eeport of 

 the British Association for 1866, include the Lingula Flags in the 

 Festiniog Group, and characterises them as ''hard siliceous sand- 

 stone with grey flaky slate, containing Lingulella Bavisii." This 

 description only applies to the Lingula Flags of South Wales. In 

 North Wales the arenaceous flags and shales containing Lingulella 

 Davisii only form a subordinate part of a series of dark-blue and 

 black, fine grained slates, containing trilobites of several genera. 



Even when we have divided the group into Upper, Middle, and 

 Lower, we have still to speak of the Upper division of the 

 Upper, and the Lower division of the Lower Festiniog, as each 

 sub-division contains two distinct sets of strata. Recent dis- 

 coveries have shown that the group includes at least six zones 

 of animal life, each distinct and separate. I believe that I only 

 meet the strict requirements of the case when I propose to form 

 three groups of the strata now included in one. My proposal is, to 

 restrict the name of the Festiniog Group to the flags containing 

 Lingulella Davisii and Hymenocaris vermicauda, to which it was 

 originally applied by Sedgwick, and to form the slates and flags 

 lying below them, characterised by typical forms of Olenus, into a 

 new group, which might well be called the Maentwrog Group, as 

 the strata included in it are exhibited in great perfection at and 

 around the village of Maentwrog, two and a half miles west-south- 

 west from Festiniog, For the blue and black slates lying above the 

 Festiniog Group, as above limited, I propose the name of the Dolgelly 

 Group, as it is only in the neighbourhood of Dolgelly that both 

 the members of which it is composed have as yet been foimd. It 

 is well characterised by several aberrant forms of Olenus, constituting 

 the genera, or sub-genera Parabolina, Peltura, Sjphoeropthalmus, and 

 Bikelocephalus of various authors. 



The Maentwrog, Festiniog, and Dolgelly Groups are both litho- 

 logically and palaeontologically distinct. None of the Crustaceans 

 pass fi'om one group to another, and peculiar genera are found in 



