The Silurian biostratigraphy of the Girvan area is reviewed. Of the 23 Silurian formations, 7 have abundant shells and 14 have common graptolites. The Silurian is nearly 3000 m thick and was chiefly deposited in a turbidite environment. All the Llandovery zones from cyphus to crenulata inclusive are represented by graptolite faunas. In the Rhuddanian (prior to the cyphus Zone) the Lady Burn Conglomerate, Mulloch Hill Formation and Woodland Formation are shelly facies laid down by a marine transgression. There are two stratigraphical breaks, the unconformity at the base of the Silurian sequence and in the Fronian, where there is a paraconformity underneath the Lower Camregan Grits, both breaks with a transgressive sequence of animal communities above them. At the top of the succession Lower Wenlock turbidites, bearing shells at their bases, are followed by a sparse ostracodbivalve assemblage representing brackish or even fresh water conditions, culminating in ‘Old Red Sandstone’ facies beds of presumably Wenlock age, all representing the marine regression seen in other inliers in the Midland Valley of Scotland. Remarkable fossil finds from the Llandovery include Stomatograptus grandis girvanensis subsp, nov., Monodimacis crenulata itself, and the only chonetid brachiopod known anywhere from the Rhuddanian or Idwlan.

SummaryFission-track dating of zircons and apatites from tuffs and bentonites has produced the first isotopic ages for the type sections of the Ordovician and Silurian Systems. In the Ordovician the following ages have been determined: lower Arenig 493 Ma, lower Llanvirn 487 Ma, lower Llandeilo 477 Ma, upper Caradoc 463 Ma and upper Ashgill 434 Ma. In the Silurian, the following: lower Llandovery 437 Ma, lower Wenlock 422 Ma, upper Wenlock 414 Ma and Ludlow 407 Ma. The Ordovician-Silurian boundary is interpreted as occurring at about 436 Ma. Three North American Rocklandian bentonites yielded zircons whose ages average 453 Ma. This is about 10 Ma younger than supposedly correlative units in the British type sections.

SUMMARY In all of 12 patients with chronic liver disease, whose platelet dynamics were investigated by the 51Cr-labelling technique in association with surface counting, platelet survival was reduced and in Ithe splenic platelet pool was increased. Surface counting showed high initial spleen:liver ratios in eight patients, and in four there was evidence of progressive destruction of platelets in the spleen. In one patient, subsequently shown to have a hepatoma, progressive accumulation of platelets was noted at the tumour site.

Ages for volcanism in the British Late Precambrian have been inferred from interpretations of SHRIMP zircon ages as follows: 559.3 ± 2.0 Ma for a tuff from the Beacon Hill Formation of the Charnian Supergroup; 566 ± 3 Ma for a tuff at Bardon Hill also in the Charnwood Forest area with abundant inherited grains at 590.5 ± 1.6; 566.6 ± 2.9 Ma and 555.9 ± 3.5 Ma for bentonite and tuff in the Stretton Group of the Longmyndian Supergroup; 604.7 ± 1.6 Ma for an ignimbrite of the Padarn Tuff Formation of the Arfon Group, and 572.5 ± 1.2 Ma for a tuff within the Fachwen Formation of the Arfon Group. These ages confirm that there were two major phases of volcanic activity in the English Midlands and Wales, one about 620–590 Ma and another about 575–550 Ma. This was followed in most of England and Wales by a major phase of tectonism before the Cambrian (Tommotian) transgression across the Midland Platform. Within the depocentre of the Welsh early Palaeozoic basin, however, sedimentation started within the second period of volcanism and may have continued without interruption well into the Cambrian Period. It is probable that the late phases of the Avalonian Orogeny lasted until after the beginning of the Cambrian. These new data show that the terranes of the Avalonian of England and Wales are comparable with those of eastern Canada and New England. The age estimate for the Charnia horizon is broadly similar to those obtained elsewhere in the world on rocks containing the earliest Ediacaran fauna and adds to the building of an extended time-scale for the global Ediacaran.

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