Vol. 67.] THE CARBONIFEROUS SUCCESSION IN GOWER. 535 



appearance, for the first time in S, of thick oolites; but, at the same 

 time, S appears, from the recurrence through it of lagoon-deposits, 

 to have been deposited in waters even shallower at times than 

 those of the S 2 oolites. 



It may be noticed that, throughout the series Z-S in Gower, the 

 junctions of the zones and subzones do not correspond with marked 

 lithological changes, except in the cases of C x with C 2 and (possibly 

 in places) of S x with S^ 1 



(vi) The change from the Modiola phase at the top of 

 S to D r — The rapid replacement of the Modiola phase by deposits 

 of open-sea, though shallow-water, facies points to rapid but not 

 great deepening; the ensuing deposits yield a D fauna, and consti- 

 tute the basal beds of the D zone. The migration of the D fauna 

 from the region where it had developed into our area appears to 

 have coincided, therefore, with a deepening. The increase of depth 

 was probably immaterial, however, for the preceding fauna was 

 ousted both over areas where standard conditions had been dominant 

 during S , even to the end, as in South- Western Gower, and over 

 those where lagoon- conditions prevailed towards the close of that 

 time, as in Eastern and North-Western Gower. 



(vii) Conditions during D x and D 2 or D 1-0 . — No rock- 

 sequence comparable with that above the Modiola phase at the base 

 of C exists in D. The initial deepening of the area of deposition 

 appears to have been slight and brief : for, once or twice during D 

 thin coals and underciay have been deposited, pointing to but little 

 depth at those times, though not necessarily to actual terrestrial 

 conditions. These shallow periods are indicated by the peaks in the 

 depth- curve in fig. 8 (p. 533). It is noticeable that, despite the 

 shallowness, a lagoon-phase has not been established, the coal being 

 intercalated among standard marine limestones. 



(viii) The change from D 2 or D 1-2 to D 2 _ 3 (Upper Lime- 

 stone Shales). — The incoming of the D 2 _ 3 fauna accompanied a 

 reappearance of shale- depositing waters : such waters had been 

 practically absent from our area since K-times. The D 2 _ 3 deposits, 

 however, were much more calcareous than those of K ; and both 

 chert and dolomite were formed in considerable amount. 



(ix) The change from D 2 _ 3 to the radiolarian phase at 

 the base of P. — In regard to depth of deposition, this change 

 resulted from the substitution of comparatively shallow conditions 

 by what appear to have been lagoon-conditions (p. 521). In regard 

 to facies of deposition, it resulted from a replacement of the cal- 

 careous (or calcareo-argillaceous) conditions that had prevailed in 

 Carboniferous times hitherto by the non-calcareous conditions — 

 whether cherty, argillaceous or arenaceous, marine or non-marine — 

 that prevailed in the South-Western Province for the rest of Car- 

 boniferous times. 



(x) Conditions during P. — Little is known with certainty 



1 In South-Western Go\ver, where the series has been most closely examined, 

 the S 2 oolites come in a short distance above the base of S 2 . 



