Introduction

During the late Caledonian orogenic cycle Laurentia-Greenland and Fennosarmatia (Baltica) became welded together along the Arctic-North Atlantic Caledonian megasuture, thus forming Laurussia, also referred to as the North Continent (Wilson, 1966; Phillips et al., 1976; Roberts and Gale, 1978; A.M. Ziegler et al., 1979; A.M. Ziegler, 1981). Late syn-orogenic and post-orogenic continental clastics, deposited in intramontane, fault-controlled depressions and also in areas peripheral to the Arctic-North Atlantic Caledonides correspond to the Old Red Sand-stone series; these range in age from latest Silurian to late Devonian (Allen et al., 1967; Friend, 1981). From these clastics the landmass occupying the central parts of Laurussia during Devonian times took its name.