Discussion

Abstract

The President said that the author’s exceedingly interesting and generally acceptable interpretation of the Ferques rocks raised a number of intriguing questions both of sedimentary environments and of regional palaeogeography. In particular, the repeated invocations of a protective off-shore reef suggested an environmental reconstruction prompted only by analogy when there was no direct evidence anywhere of reef-in-place: no doubt a number of stromatoporoids may have formed an incipient reef-assemblage, but comparison with the Belgian Devonian reefs would suggest local patch reefs rather than reef-carriers protecting a back-reef lagoon. In terms of the usual fossil associations in which spirifers are found it would similarly be unlikely that they massed together in packed ‘reef’—certainly not in an intertidal zone; and a calcareous algal mat lying along a littoral margin of a terriginous flood plain is perhaps a less probable habitat than an off-shore mat (or off-shore patches) repeatedly torn and fragmented by waves and thrown shorewards during storms. A more general problem was the relation of the Ferques rocks with the nearby Devonian rocks of south-east England. The Caffiers conglomerate spectacularly defined a mid-Devonian Brabant massif; but there was little sign of such a landmass in Britain, and even less of a marine transgression like that of the Boulonnais Frasnian and Famennian. The Old Red Sandstone of the East Anglian platform (including its flanks beyond Cambridge and towards London) was generally of ‘Welsh’ type: even when it was marine (in sediments of Middle and Upper Devonian age) the analogies were with