XXV.— The Liassic Sequence in Morvern

Abstract

1. General Account The sedimentary succession in Morvern, ranging in age from Carboniferous to Cretaceous, has been described in the Geological Survey Memoir on “The Pre-Tertiary Geology of Mull, Loch Aline and Oban” (Lee and Bailey, 1925). Later contributions to the study of these rocks have been made by Scott (1928), Lee and Pringle (1932), Macgregor and Manson (1934; Carboniferous only) and Richey (1935). The Jurassic is represented by beds of Lower Lias age only, but these are well-developed and on the basis of ammonite remains the Survey has established in them the existence of the following zones: rotiforme, bucklandi, semicostatum, birchi and obtusum. The presence of the birchi zone, somewhat tentatively indicated in the Survey Memoir (p. 79), has been confirmed by the evidence of fossils recently obtained by the present writer. The Lias of Morvern which, like other Mesozoic rocks in the West of Scotland, owes its presence to the protection of Tertiary lavas and to some extent to faulting, is irregular in its distribution and varies considerably in thickness over short distances; it attains locally a maximum thickness of a little over 200 ft. The succession is divided by the Survey on a lithological basis into a lower series of alternating limestones and shales, the Broadford Beds, and an upper series of shales, sandy shales and shaly sandstone known collectively as the Pabba Beds. The most complete section is that seen in the Allt Leacach on the east side of Loch Aline (Figs. 1 and 2). In This 250-word extract was created in the absence of an abstract