Vol. 67.] THE CARBONIFEROUS SUCCESSION IN GO WEE. 497 



Province, is well-defined lithologically and, in a sense, palaeonto- 

 logically also, the unfossiliferous, ' continental ' Upper Old Red 

 Sandstone giving place, rapidly but conformably, to the fossiliferous 

 marine Avonian. The junction, as exposed in the Fairyhill dingle 

 and recorded, with details of the adjacent beds, in the West Gower 

 Memoir (p. 8), is as follows. The top of the Upper Old Red 

 Sandstone is a barren, red marl with limestone-nodules (' race , ). 1 

 The base of the Avonian is a grey, sandy limestone with limestone- 

 fragments, some of which are red like the k race ' in the under- 

 lying marl, the rest being, doubtless, practically contemporaneous. 

 In the matrix between the fragments are a few ostracods and 

 ooliths, and the bed is followed immediately by the 'sandstone with 

 modioliform lamellibranchs ' previously mentioned. The junction 

 of the Old Red with the Avonian is so sharp as to be clearly 

 traceable in a microscope-slide [E. 5288, Geol. Surv. Colin.] ; and 

 though it partly owes its conspicuousness to the difference in 

 colour between the beds above and below, this difference is but 

 the outward sign of a fundamental change in the conditions of 

 deposition, marine organisms appearing in the rocks immediately 

 above. In Gower, it may be noted, the change (which is inferred 

 to be conformable from a merging of the top of the Old Red into 

 the Avonian) is almost abrupt, and has been accompanied by 

 current-action, as is evident from the fragments at the junction; 

 in some parts of the South-Western Province, on the contrary, as 

 for instance in Pembrokeshire, 2 marine and continental conditions 

 alternated for a space. 



The junction of Km with Group 2 of K x and that of K 2 with Z 

 do not appear to be exposed. The limestone-group (3) probably 

 separates K 1 from K„ for it is exactly similar, lithologically, to the 

 limestone that affords the best boundary between these two sub- 

 zones in Pembrokeshire. 



Zaphrentis Zone, Z, — Cherts are found, though only now and 

 then, above the group of limestones with cherts near the base of 

 the zone. 



Syringothyris Zone, C. — The Caninla Oolite is partly 

 dolomitized at various horizons up to the top, the matrix between 

 the ooliths being the material chiefly affected. In places, the rock 

 has been partly silicified, the silica taking the form of numerous 

 aggregates of microscopic quartz-crystals ; unlike the dolomite, 

 these replace ooliths and stop at the interstitial matrix. 



The top of the Oolite is uneven, the irregularities reaching a 

 depth of a foot or more. But the hollows are not in all cases 

 simple depressions ; some extend into the Oolite laterally and are 

 overhung by roughly-horizontal tongues of it measuring up to a foot 



1 The red marl, to a thickness of 4 feet, rests upon unfossiliferous, pebbly, 

 grey quartzite which is probably the top of the thick quartz-conglomerates 

 that form the upper part of the Upper Old Eed of Gower (West Gower Memoir, 

 p. 5). 



2 ' Summary of Progress for 1908 ' Mem. Geol. Surv. 1909, pp. 35-36. 



