Discussion

Abstract

The P resident commented that the hitherto unsuspected Bohemian element in the lower Wenlockian zones was of considerable interest. Written contribution from Dr G. Y. C raig and Dr E. K. W alton : We should like to inquire how firmly the three new graptolitic zones recognized are based. Are the diagnostic graptolites abundant? Are they well preserved? In our experience in Kirkcud-bright most of the graptolites are in a very poor state of preservation. We understand that the mapping of the boundaries of the new stratigraphical divisions depends almost entirely on the presence of the fossils. Are the graptolitic bands throughout the succession sufficient in number to allow precise positioning of the boundaries, or are there broad zones of uncertainty? The stratigraphical position of the Hawick rocks remains a puzzle. Part of the difficulty arises from poor definition originally by Lapworth and Wilson, but the main problem is lack of fossils. This latter has been partly overcome in the last few years in Kirkcudbrightshire and Wigtownshire where Mr Rust and ourselves have found a number of graptolite bands in beds previously taken as Hawick rocks. The fossils suggest a Valentian age, thus throwing doubt on Dr Warren’s hypothesis and a previous suggestion of ours that the Hawick rocks were younger than the neighbouring Riccarton Beds. The fossil bands however occur in strata without red beds and typical Hawick rocks with red beds lie to the south-east, occupying a band about 6 miles across the strike. This 6-mile stretch has still proved to be