BOOK REVIEWS

Regional Geochemistry of Parts oJ" North-West and three-component Ni-Cd-Zn in the S part of and North Wales. Keyworth, the I)enbigh Moors; an Y anomaly associated Nottingham (British Geological Survey), 1997. with igneous rocks at Pen-y-Bedw, S of Betwys- vii + 128 pp (with maps and an overlay in pocket). y-Coed; Cu and Pb with three three-component Price, s ISBN 0-85272-307-5. maps for Snowdonia; and maps of the distribution of Cu and of the three components Cd-Ag-Zn and This, the twelfth volume in the series, presents Sb-As-Bi for the Parys Mountain area of baseline geochemical data over an area ranging Anglesey. from the Forest of Bowland and the western The final double-page spread contains a map Pennines, the drift-covered plains of Lancashire for Cu and six three-component maps tbr various and Cheshire (including the urban and industrial heavy metals in the contaminated soils of belt of and Liverpool), and northern Lancashire, chiefly to the west of Manchester. Wales, including the Denbigh Moors, Snowdonia, Here the low-lying land mainly in the floodplain Anglesey and the IAeyn Peninsula. After an of the , and underlain by glacial and introductory section detailing the methods of fluvial sand and gravels, was formerly occupied sample collection and preparation, chemical by fens (locally known as 'mosses') in which peat analysis, statistical information and data intepreta- deposits developed after the last glaciation. tion, there is a useful summary of the geology of Drainage reclaimed most of this land for the area accompanied by a simplified geological agricultural and industrial use (including the map. This is followed by a brief but important Liverpool and Manchester railway), and the description of the mineralization and mining town of lrlanl had iron and steel works, a large (ranging from coal, slate and rock salt to volcanic coal-fired power station, major gas and sewage massive sulphide base-metal deposits, red-bed works and a large chemical factory. The very high Cu-Ba mineralization in Triassic sandstones, and levels of several heavy metals tbund in the soils of stratiform volcanogcnic manganese deposits on and Carrington Moss (and also Halsall the Lleyn Peninsula): this is usefully accompanied Moss NW of Onnskirk) reflect the historical use by a map showing the locations of the various of these mosses for the disposal of Manchester's mineral deposits and brief details of the elements 'street waste', transported down the Ship Canal in or commodities mined. barges, distributed over the area of the mosses and The collection of multicolourcd maps opens by ploughed in. This combination of peaty soil and illustrating the geochemistry of stream water, with organic and mineral waste produced a rich fertile individual maps for acidity, conductivity, and the soil which was used for growing vegetables until levels of bicarbonate, tluoride and uranium. These the 1950s. There is some indication from the are followed by a series of maps displaying the metal levels that furnace slag and power-station geochemistry of 31 individual elements in stream ash was also disposed of in this fashion. sediments, and by a further batch of maps of the A feature in this volume is the enclosure, at the individual elements in soil samples (all on a scale back, of 1:250 000 maps of not only outdoor of 1:500 000). These are succeedcd by 14 maps gamma-ray radiation based on solid geology but showing multi-element geochemistry, ranging also of radon potential based on solid and drift from Mg:Ga and La:Y ratios in stream sediments geology, both for 'Liverpool Bay', which in fact to five sophisticated three-component colour includes most of the area covered by the rest of composite maps of, tbr example, Fe-Mn-Co in the volume apart froln Ang]esey, the Lleyn stream sediment, followed by a series of smaller Peninsula and parts of Snowdonia. The radon scale maps demonstrating the geochemical potential was calculated by log-normal modelling, signatures of black shales in the Craven Basin based on the interpretation of radon measure- contrasted with those of the Llanrwst mining area ments in dwellings and soil-gas radon measure- and the Valc of Conwy (single element maps for ments, supplemented where data were sparse by Cu and Ag together with a Mo-U-V three- assessment of rock and geochemical evidence. component map); the distribution of Be, Cd, Ni The rocks with the highest radon potential in this BOOK REVIEWS

map area are the Carboniferous Limestone in morphic petrologists for their entire careers, the North Wales and around Clitheroe, and the coverage is patchy. Nevertheless, there are some Namurian and certain acid intrusive rocks in excellent chapters here which present the results North Wales. The Permo-Triassic rocks under- from some of the most exciting work going on in lying much of the Manchester and Liverpool areas the field. While readers of a philosophical bent have uniformly low radon potential. Surprisingly, will like Hodges' Gaia-like view of the Himalayas perhaps, there is no mention of selenium in soils as a self organising system, I particularly enjoyed of the agricultural areas covered. the modelling study of Barrovian metamorphism Altogether this volume is extremely informative, by Jamieson and her colleagues. This coupled dealing as it does with an area where the geological thermal and mechanical model is presented with map alone can only give part of the story, because an honest account of its limitations, but nicely of the extensive spread of mining and industrial demonstrates the importance of the balance debris and contamination. The map of radon between subduction and radiogenic heating in potential will be of considerable interest, and the the thermal development of an orogen. degree of heavy-metal contamination in the soils to Another paper that I found very valuable is that the west of Manchester should serve as a Warning by Sandiford & Hand on the high-T, low-P to future generations. The areas covered by metamorphism of the Australian Proterozoic. published atlases in this series are creeping steadily Most examples of such metamorphism are south; it will be useful to have coverage of the clearly associated with contemporaneous magma- whole of Great Britain on this scale. tism, and lead to the old debate about the R. A. Howm distinction between regional and contact meta- morphism in situations where volcanism means that the magmatic heat input to the upper crust ['reloar, P.J. and O'Brien, P.J. (Eds). What Drives was much greater than that contributed by the Metamorphism and Metamorphic Reactions? plutonic rocks remaining today. However there London (The Geological Society, Special are a few areas, and this is the best known, where Publication No. 138), 1998. vi + 287 pp. Price geochronology stubbornly refuses to support such s ISBN 1-86239-009-6. a simple association, and these authors have produced a conductive heating model, based on Understanding the causes of metamorphism has the presence of anomalously radiogenic material been one of the major objectives for metamorphic in the crust. The more normal association of high- petrologists throughout the 20th century. Progress T, low-P metamorphism is discussed by Brown in has been remarkable despite a few wrong the context of the classic Ryoke and Abukuma turnings, from the invention of geothermometry belts of Japan. These have been interpreted as by Goldschmidt in the early years of the century, having formed in the roots of an arc for many through Eskola's facies principle to the recogni- years, but Brown argues that it is actually ridge- tion by Miyashiro, first that different patterns of trench interactions which cause such meta- metamorphic facies corresponded with different morphism, through the more voluminous basic thermal gradients in the crust, and subsequently volcanism that results. It is certainly an important that these could be identified with different plate point to recognize that on a spherical earth, triple tectonic settings. Contrary to the impression given junctions may migrate through any one point by the editors of this volume in their introduction, during the evolution of an individual belt, but the the developments of the last 20 years have largely specific evidence for ridge involvement seems to been in the detail, but this work is gradually remain elusive. Certainly in the example with bringing us to a much more complete and which I am most familiar, that of Connemara in dynamic view of orogenesis, tracking tectonics the Irish Caledonides, the arc was recognized in and structure, heat and burial, through time. the first place in the early 1980s precisely because Despite the breadth of its main subject, this the mineralogy and chemistry of the basic book also finds room to include papers that deal intrusions had unequivocal arc characteristics. with metamorphic processes and reaction Back then we would have been much less certain mechanisms, and one that does not seem to have if there had been a MORB signature to confuse much to do with either theme. the issue! Inevitably, with just 14 chapters to review most A final paper of note in this part of the volume, of what has interested most of today's recta- which also includes several meticulous case

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