Abstract
IN this useful little work, Mr. Harker has given an admirable résume of the results which have, up to the present time, been arrived at by the study of the ancient igneous rocks of North Wales. Besides summarizing the work of the late John Arthur Phillips and E. B. Tawney, of Prof. Bonney, Mr. Rutley, Mr. Cole, Mr. Teall, Mr. WaIler, Miss Raisin, and others who have written on the petrography of the district, he has added many new and often judicious notes on the rocks in question. A number of fresh analyses, and the description of hitherto unrecognized varieties of rocks and minerals, raise the Work out of the category of mere compilations; and the excellent classification and arrangement of his materials make the book one eminently useful for purposes of reference. It is unfortunate that it has no index, though the “table of contents,” which is very full and carefully paged, causes the want to be less felt than it otherwise would be. Mr. Harker classifies the districts of Caernarvonshire in which volcanic rocks are found as the Eastern, North-Western, and Western, the latter consisting of the Lleyn peninsula. He groups the types of rocks represented under the headings of “rhyolitic lavas,” “nodular rhyolites,” “acid intrusives,” “intermediate rocks,” “diabase sills and basalts,” and “other basic intrusions.” The work concludes with a “review of vulcanicity in Caernarvonshire,” in which we find discussions of the relation of the volcanic eruptions to the earth-movements that took place at the period of their occurrence, the succession of lavas in the district, and the evidence in favour of their submarine origin. The book is admirably printed, and is illustrated by six very clearly-drawn sketch-maps. The essay is worthy of the memorial in connection with which it appears, and is creditable to the University under whose auspices it is issued; and higher praise than this it would be difficult to give to any work of the kind.
The Bala Volcanic Series of Caernarvonshire and Associated Rocks; being the Sedgwick Prize Essay for 1888.
By Alfred Harker, M.A., F.G.S., Fellow of St. John's College, and Demonstrator in Geology (Petrology) in the University of Cambridge. (Cambridge University Press, 1889.)
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The Bala Volcanic Series of Caernarvonshire and Associated Rocks; being the Sedgwick Prize Essay for 1888. Nature 41, 414 (1890). https://doi.org/10.1038/041414a0
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DOI: https://doi.org/10.1038/041414a0