Vol. 67.] THE CARBONIFEROUS SUCCESSION IN GOWER. 501 



The boundary between Z l and Z, was not located, but is evidently 

 not marked by any striking lithological change ; the top of Z„ also, 

 is not conspicuous, as nodular and argillaceous beds, though most 

 characteristic of Horizon y above, commence in the highest part of Z 2 . 



The most complete and accessible section lies between the core' of 

 the Worms-Head anticline, at a level somewhere in Z 1 (see preceding 

 footnote), and the edge of the cliff at the Coastguard Station to 

 the north-east, which exposes the top of the zone and a few yards 

 of the overlying y beds. Here at least 530 feet (a figure obtained 

 largely by direct measurement) is exposed, but in this district the 

 full thickness of the zone cannot be determined. 



Horizon y and Syringothyris Zone, C. — The chief points 

 to be noticed in this part of the sequence are : — 



(1) Horizon y is -well developed ; 



(2) The Laminosa Dolomites are but partly doloinitized, and contain cherts 



and beekitized fossils ; 



(3) There is no Modiola phase at the base of 2 ; 



(4) The l'aoies of C 2 resembles that of the standard C 2 -limestones of the 



Eastern District, not that of the North-Western District, 



(1) Horizon y consists of thinly bedded, nodular limestones with 

 soft argillaceous partings ; this character is most marked in the upper 

 part. Fossils, especially corals, abound ; they are magnificently dis- 

 played on extensive, weathered surfaces at Tears Point — the best 

 Avonian collecting-ground in Gower, but unfortunately discovered 

 too late for its fauna to be recorded. 



The base of Horizon y, defined as the level at which large 

 Caninids first become frequent, may be placed, to facilitate recog- 

 nition, at a rather marked argillaceous bed which reaches the sea 

 at Tears Point. The summit was placed, arbitrarily, but merely 

 for the purpose of measurement, at the lowest of the dolomites 

 which are the feature of the overlying Laminosa Dolomites, for 

 in the absence, so far as could be seen, of Chonetes cf. comoides 

 (Sow.) from the Laminosa Dolomites, there did not appear to be any 

 important faunal difference between this group and Horizon y. 



(2) The lower part of the Laminosa Dolomites (for thickness, 

 see the table on p. 502) consists of about equal proportions of dolo- 

 mites of the usual character and of unaltered limestones ; the lime- 

 stones are rich in corals, and contain also some crinoid-cups. The 

 upper part is normal in its dolomitization, but includes occasional 

 chert-nodules and beekitized fossils. The change at the top to the 

 Caninia Oolite is rapid, that is, the thickness of dolomitized oolite at 

 the junction is small, and so too in North-Western Gower. 



(3) Standard C 2 limestones follow the Caninia Oolite immediately. 

 Their basal bed is firmly welded to the somewhat uneven top of 

 the latter, and contains small masses of oolite (the outcome, doubt- 

 less, of a little contemporaneous erosion), which are mixed with 

 broken brachiopods, corals, etc., proper to C 2 . 



(4) The C 2 limestones are largely light-grey and thickly-bedded, 

 and are less crinoidal than many parts of Z ; probably fewer 

 dolomites and gasteropod-beds are intercalated than in (J 2 of 



