Part I. Stratigraphy

Abstract

The two outstanding achievements of Lapworth's work were the demonstrations, first, that previous stratigraphical arrangements included tectonicaUy duplicated and even triplicated parts of a general succession which, contrary to general belief, could be correlated with those of structurally less complicated areas; and secondly, that this assorted succession, estimated by him to be almost 3000 ft. thick, was equivalent to about 100 ft. of graptolitic shales exposed in the Central Belt of the Southern Uplands. These relationships are well summarized by Peach & Home (1899, pp. 82-3), who accepted Lapworth's succession with no more than minor revisions of formational thicknesses and the transference of the Balclatchie Mudstones, Grits and Conglomerates from the top of the Barr Series to the base of the Ardmillan Series. In effect, all the difficulties experienced by earlier geologists were shown to be due to an inadequate appreciation of the importance of fossil faunas and facies changes, not only in determining successions but also in resolving the structure of the region. Yet, paradoxically, Lapworth paid scant attention to either faunal or lithological changes when preparing his interpretation of the Caradoc sequences, mainly because he believed the Benan Conglomerate to be a reliable datum horizon (1882, pp. 551,659). By using the formation in this capacity he showed that three belts of limestones, exposed around Benan Hill, were not impersistent lenses within a thick conglomerate but simply one limestone member underlying the Benan Conglomerate and brought to the surface by folding. With regard to this particular section he was