General discussion

Abstract

M. G. Bassett ( National Museum of Wales, Cardiff , CF1 3NP, U.K.). Professor Holland’s emphasis on the refinement of a stratigraphical framework to improve correlation and recognize synchroneity of events through the late Silurian-early Devonian interval is especially pertinent when linked to Professor Allen’s description of the physical changes involved in the transition from marine to non-marine environments. The suturing of Laurentia and Baltica to form the ‘Old Red Sandstone continent’ was important in establishing for the first time in the Phanerozoic extensive and persistent terrestrial areas, whose relevance to biological evolution and colonization of the land are discussed elsewhere in this symposium. Dating of the marine to non-marine transition throughout the Caledonide Orogen is now sufficiently refined to demonstrate clearly that this was by no means a synchronous event, but extended at least from late Llandovery-early Wenlock times until the early-mid Devonian.