Vol. 67.] THE CARBONIFEROUS SUCCESSION IN GOWER. 525 



content, or a reduction of temperature. 1 Neither its muddiness 

 nor its probable shallowness would account for the faunal change, 

 as similar influences had previously had no such effect, even 

 when acting in conjunction, as during Km. But, whatever may 

 have been the nature of the change in the sea, its radical 

 character and the wide extent of the area affected point to an 

 important change in the physiography of the region. Further, there 

 is reason to believe that the change in the sea accompanied a 

 marked increase in the influence of the waters from a neighbouring 

 river (p. 539). And that radiolaria may abound in an area under 

 such influence appears to be shown by their occurrence in quantity 

 in the Lower Culm of Eastern Thuringia and the Yogtland, which 

 is regarded, from the abundance of land-plants that it contains and 

 for other reasons, as having been deposited in a muddy sea near the 

 mouths of rivers. 2 * 



(5) Topographical Position of Lagoon-Areas. 



That the areas of deposition of the Modiola phases of Gower 

 were situated, probably in each case, immediately between the coast 

 of the Avonian sea, which lay to the north throughout the South- 

 western Province, and the open water may be inferred from the 

 following details, partly outlined in Table Y, 2, p. 526. In arriving 

 at this conclusion, true overlap of a phase by conformable higher 

 beds is accepted as evidence that the lagoon-area in which that 

 phase has been deposited has been limited by a shore-line along 

 the line of overlap ; while lateral replacement by ordinary marine 

 sediments is accepted as evidence of the deeper-water limit of the 

 area. For this reason a lagoon-area has been defined (p. 512) as 

 essentially coastal. 



The lagoon-phase at the base of K in Pembrokeshire 

 overlaps the conformable Upper Old Red Sandstone in a northerly 

 direction, and is itself in turn overlapped by conformable higher 

 beds, which then rest directly upon Lower Old Red Sandstone or 

 upon still older rocks. The deeper-water limit, also, of the lagoon- 

 area appears to be reached in that county : for, at Freshwater West 

 in the southernmost outcrop, the Upper Old Red Sandstone is 

 followed immediately by ordinary marine sediments in which no 

 lagoon-deposits have yet been found. 



The lagoon-phase at the base of C 2 + S 1 in Pembrokeshire 

 succeeds the Caninia Oolite conformably south of West William- 

 ston, but at that place an unconformity develops at its base. 

 The proximity of the lagoon-area to a shore-line, thus suggested, 

 appears to have persisted throughout the phase, for at Pendine 



i L. W. Collet, ' Les Depots marins ' Paris, 1908, pp. 10-22 & 219. 

 2 J. Lehder, Neues Jabrb. Beilage-Band xxii (1906) pp. 79-80, 111. 



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