Vol. 67.] THE CARBONIFEROUS SUCCESSION IN GOWER. 531 



possess features linking them so closely with the Gower cherts that 

 they, also, may be inferred to have been formed under lagoon- 

 conditions. As an example may be cited the Gondwana plant-beds 

 with radiolaria, described by Dr. A. K. Coomaraswamy 1 as having 

 been ' deposited in comparatively shallow water.' They resemble 

 the Gower cherts in their fine grain and very thin bedding ; and, 

 like various lagoon-phases, they occur near the base of a trans- 

 gressing series, for they lie a short distance above gneiss, from 

 which they are separated by merely a small thickness of sand- 

 stone, etc. 



The close connexion between the development of lagoon-areas 

 and certain earth-movements, discussed in the preceding section, 

 and their locus on coastal shelves are related, possibly, to the fact 

 that some Modiola phases, such as the Burdiehouse-Limestone 

 Group, have been accompanied by volcanic outbreaks, including 

 the effusion of lavas which possess a pillowy structure, 2 though the 

 available data are insufficient to show whether such outbreaks have 

 been connected with Modiola phases to a greater extent than with 

 the contemporaneous standard deposits. 



In this connexion, however, it is important to note that radio- 

 larian cherts in various parts of the world are frequently accom- 

 panied by volcanic rocks, especially lavas possessing a pillowy 

 structure ; and, as bearing on this aspect of the subject and the 

 views which I have ventured to put forward, the following words 

 of Prof. Charles Lapworth are significant. Speaking of a hypo- 

 thetical area on which radiolarian cherts and associated igneous 

 rocks might be supposed to have been deposited, he said 3 : — 



' Consider, for example, such an area as originally forming part of a slightly 

 submerged continental shelf, or coastal platform, with volcanic and archi- 

 pelagic conditions, and overlooking a broad and deeper sea. Suppose, 



further, the platform itself floored by rocks already metamorphosed, and that 

 this platform remains covered by shallow waters for an extended period of 

 geological time, while the sea-flour in front of it is continually deepening. 

 Under these conditions, only such mechanical, volcanic, or organic material 

 could become accumulated as rock-layers on the submerged platform, as by 

 their original nature or rapid cementation were incapable of being swept off 

 by the waves and currents of the shallow waters into the open and deepening 

 sea beyond. Such rock-formations as would be accumulated on the platform 

 would necessarily be thin, but would be lithologically varied and peculiar.' 



This graphic passage, with certain modifications, embodies the 

 general conclusions to which I have come as to the situation in 

 which lagoon-phases, so 'varied and peculiar ' in their features, have 

 been deposited. The chief difference lies in my interpretation of 

 some of those features ; they point to the dominance of compara- 

 tively still water within the shallow area. 



1 Geol. Mag. 1902, p. 305 ; see especially p. 306. 



2 Sir Archibald Geikie, ' Central & West Fife & Kinross' Mem. Geol. Surv. 

 1900, p. 54. 



3 Q. J. G. S. vol. lviii (1902) p. 440. 



