The object of the present communication is to demonstrate the relationships which, in the light of present knowledge, appear to exist between the various Pleistocene and Holocene deposits in the Lower and Middle Thames Valley. For this purpose two cross-sections of the valley have been drawn indicating the relative positions of the deposits which occur at various localities as though they were all present in two localities, one in the Lower, and one in the Middle Thames.As many of the more important deposits in the Lower Thames are represented to the north and south of the river in the Dartford area, we have drawn the one section as if our ideal locality occurred in that neighbourhood. In this section, therefore, the relative altitudes of the various beds above and below present river level are those which are found in that part of the Thames basin. In tributary valleys, or in other parts of the main valley these altitudes are not of course necessarily maintained. In cases where deposits belonging to a particular stage have not been preserved in the Dartford area, but occur in a neighbouring part of the valley, or in a tributary valley, their position in the composite section has been roughly gauged by a process of extrapolation. Similarly when dealing with the Middle Thames, we have drawn our ideal section as though all the deposits occurred in one section of the valley in the neighbourhood of Iver.

The neural cell adhesion molecule (N-CAM) is a complex of surface glycoproteins that are developmentally regulated and believed to be intimately involved in the orderly structuring of the CNS. Here the effect of chronic low-level lead exposure on their expression in the postnatally developing cerebellum is described. Rat pups were chronically exposed to lead via their dam's drinking water which contained either 200 or 400 mg PbCl2/L from time of birth. Pup postnatal blood lead levels ranged between 10 and 20 micrograms/dl until day 16 after which they became elevated to 40 micrograms/dl on day 20. During this period the developmental sialylation state of N-CAM, which is believed to regulate cell-cell interaction, fibre outgrowth, and synapse formation, was monitored by rocket immunoelectrophoresis. In control animals the expected desialylation of N-CAM was found to occur at times coincident with postnatal synaptogenesis. In contrast, desialylation in animals chronically exposed to lead was found to be significantly impaired when blood lead levels exceeded 20 micrograms/dl. This could not be attributed to lead-induced undernutrition or alterations in immunoprecipitate formation. These observations could account for the neurobehavioural deficits that are known to be induced at similar blood lead levels, and the potential contribution of impaired N-CAM desialylation to synaptic elaboration is discussed.

The area to be described is part of North-Western Montgomery- shire. All place-names mentioned will he found on the 1-inch Ordnance Survey Map, Sheet 136 (Bala). or on the accompanying sketch-maps (figs. 1, 2, & 3, pp. 488, 493, & 496). Geologically, this area is the western part of the southern flank of the great Berwyn dome of Ordovician strata; hut a glance at the geological map shows that in this south-western portion the beds are pinched up so as to form a wedge-shaped south-westerly extension, one flank of which runs with remarkable straightness for several miles. The reason for this straightness of outcrop lies in the fact that in this belt of country the strata are vertical, or have acquired a slight reversal of dip from the south-eastward overfolding. To this cause must also be attributed the parallel arrangement of hill and valley, each band of hard rock standing out as a straight ridge, and each soft bed forming a parallel depression. Thus the sandstones of the Caradocian and the grits and massive mudstones of the Salopian stand out as ridges, while the softer Ashgillian and the sliales of the uppermost Caradocian form the marked valley which is followed by the old pack-road connecting the Upper Vyrnwy valley with that of the Tanat. This strike-valley is drained by various streams. In its northeastern part to Pen-y-garnedd (Sheet 137 it is drained by a tributary of the Tanat, then for a short distance the headwaters of the Cain drain the

The fossils described below were collected by Messrs. B. K. N. Wyllie, Keir A. Campbell, and G. M. Lees, working on behalf of the Turkish Petroleum Company, who have kindly made arrangements for me to investigate their collection, which proves to be of some interest.

No abstract