Vol. 67.] THE CARBONIFEROUS SUCCESSION IN GOWER. 519 



and Galcisphcera (?) in abundance; but at many places one or 

 two members only are found. The lack of standard fossils in 

 the mudstones is striking in the case of the phases that we are 

 considering : for the latter occur in a formation, the Avonian, 

 dominated by crinoids and other open-sea forms. A few mud- 

 stones, however, as, for instance, some at the top of S 2 , contain 

 many individuals (though but few species) of brachiopods, especially 

 Seminida, that lived under standard conditions also. Again, the 

 proximity of the postulated lagoon-areas to the open sea with its 

 abundant fauna, and their liability to invasion, account for the 

 abundance of standard forms in the intercalations of ordinary 

 rock-types, which are frequent in some phases (Km and the top of S 2 ). 

 The S 2 ' pisolites,' also, have been laid down in disturbed waters, 

 and yield an ordinary marine fauna. It may be noted that, in 

 the phase in C + S 1? intercalations yielding open-sea forms are 

 extremel) rare. 



The phasal fauna is essentially shallow-water, but its poverty 

 and peculiar nature demand for full explanation something more 

 than mere shallowness. The isolated position in which the mud- 

 stones must have been deposited — whether separated from deeper 

 water simply by extensive shallows or by actual barriers — would be 

 favourable either, under certain circumstances, to an increase of 

 salinity, or, near a river, to a freshening of the waters. In either 

 case much of the standard fauna would be excluded. Some 

 ostracods, like their modern representatives, doubtless could endure, 

 and even thrive under, such adverse conditions. The same appears 

 to have been true of other organisms also. Thus, although lagoon- 

 conditions would favour the accumulation of plankton, including 

 Ccdcisphcera (1 ) , simply on account of its ease of transport from 

 the open sea outside the lagoon-area, the fact that some of the 

 calcite-mudstones contain an abundance of Ccdcisphcera (?), but 

 fewer or no foraminifera, whereas standard Avonian limestones 

 (including those deposited in shallow water) yield these two groups 

 of organisms in inverse ratio, suggests that Calcisplicera (? ) throve 

 in the lagoons. 



But, whether due to more than mere shallowness or not, the 

 characteristic feature of the calcite-mudstones, the most distinctive 

 rocks of the calcareous lagoon-phases of Gower, is barrenness or a 

 peculiar fauna, rich in individuals but not in species, which, though 

 but poorly represented in intervening standard deposits, is re- 

 markably recurrent, as regards genera and wider groups, in different 

 phases. 



(3) The Radiolarian Phase — Cherty Lagoon-Phase— 

 of Gower. 



Modes of origin of radiolarian deposits. — The fourth 

 lagoon-phase, that at the base of P, consists of radiolarian cherts 

 with interbedded, laminated shales which have yielded a few 

 lamellibranchs and plant-fragments. As, however, many radio- 

 larian rocks have, in consequence of the classic work of Dr. G. 



