Previous studies of low-grade metamorphism in the Southern Uplands accretionary terrain indicated prehnite-pumpellyite facies/anchizone conditions developed throughout the area, except for local preservation of trench-slope sediments and an accreted seamount at zeolite facies/advanced diagenetic grade. New graptolite reflectance data are presented that show a general northward increase in temperature in the Southern Uplands. The results from two cross-strike traverses in the southern and central belts in contemporaneous sequences, using illite crystallinity, illite lateral spacing (b o) , and graptolite reflectance, indicate the development of systematic accretion-related low-grade metamorphism. Well-developed and constant anchizone conditions occur throughout the NE (Langholm) traverse, associated with common, F1 accretion-related folding and a regionally penetrative S1 cleavage. In the SW (Kirkcudbright) traverse, however, the youngest, last accreted packets are preserved at a transitional diagenetic stage and lack a penetrative S1 cleavage. Illite crystallinity, graptolite reflectance, and b o increase systematically northward through earlier accreted packets, reaching values of the NE traverse only at the northern end. The concomitant increase of b o with illite crystallinity suggests the relatively high P-low T trajectory characteristic of subduction zones. Integration of metamorphic and structural data relates increasing intensity of aceretion-related F1 folding, developmertt of S1 fabric, and onset of later fold phases to grade of metamorphism and structural level within the accretionary pile.

Graptolites are common fossils in Early Palaeozoic strata, but little is known of their soft-part anatomy. However, we report a long-overlooked specimen of Dicranograptus aff. ramosus from Late Ordovician strata of southern Scotland that preserves a strongly polymorphic, recalcitrant, organic-walled network hitherto unseen in graptoloid graptolites. This network displays three morphologies: proximally, a strap-like pattern, likely of flattened tubes; these transform distally into isolated, hourglass-shaped structures; then, yet more distally, revert to a (simpler) strap-like pattern. The network most likely represents a stolon-like system, hitherto unknown in graptoloids, that connected individual zooids. Its alternative interpretation, as colonial xenobionts that infested a graptoloid colony and mimicked its architecture, is considered less likely on taphonomic and palaeobiological grounds. Such polymorphism is not known in non-graptolite pterobranchs, which are less diverse and morphologically more conservative: a division of labour between graptoloid zooids for such functions as feeding, breeding and rhabdosome construction may have been the key to their remarkable evolutionary success.

Charts are presented showing the correlation of graptolite biozonations for the Lower Ordovician to Lower Devonian, i.e. for the entire stratigraphical range of the planktonic graptoloid graptolites. Regions chosen are those for which the most detailed biostratigraphical studies have been undertaken. For Baltica, average graptolite zone (chron) duration appears to vary from c. 300000 years (Ludlow Epoch) to 2.4 Ma (Lochkovian Epoch).

All trilobites known from the Ardwell Group, Craighead Inlier, Girvan district are listed and frequencies recorded. Encrinuroides lapworthi n. sp. from the Sericoidea Mudstones, and Bumastoides fornax n. sp. from the Kiln Mudstones, are described. The Sericoidea Mudstones constitute a deeper water interlude in the complex succession which comprises the Craighead Limestone Formation; graptolites from this horizon indicate low Dicranograptus clingani zone. The closest resemblance of the trilobite assemblage as a whole is to faunas of Trenton age in North America. The occurrence of forms allied to Boda Limestone (Ashgill) species suggests that these are long-ranging, carbonate associated, trilobite stocks.