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 A HISTORY OF SURREY To illustrate the position in the wider geological scale of the forma- tions recognized in Surrey, we give below, as preliminary to the next table, a summary of the full succession of rock-systems according to the commonly-adopted classification, indicating which divisions are already known to exist in the county. Classification Rock-systems Relation to Surrey Recent Fairly represented Pleistocene Partly represented Cainozoic Pliocene Doubtfully represented or Tertiary Miocene Absent Oligocene Absent Eocene Widely represented Upper Cretaceous Widely represented Lower Cretaceous Widely represented Upper Jurassic Not yet proved, but almost certainly under- Mesozoic or Secondary Middle Jurassic lying southern part of county In part represented in deep borings in north of county Lower Jurassic Not yet proved Triassic Possibly represented in deep borings in north of county (see p. 21) Permian Carboniferous Palaeozoic Devonian Not yet proved ; but some part certain or Primary Silurian. to exist deep underground Ordovician Cambrian Eozoic and Pre-Cambrian Azoic (?) Archaean We may now turn to consider the classification and subdivision of the known strata of the county, as shown in the following table, including those which crop out at the surface and those which have been found only in deep borings. Valley, vol. i., by W. Whitaker (1889), for later information respecting the Eocene, the River Drifts and other superficial deposits, and for discussion of the deep borings and deep-seated geology, and vol. ii. of the same memoir for details of Surrey well-sections ; The Cretaceous Rocks of Great Britain, vol. i., by A. J. Jukes-Browne (1900), for the Gault and Upper Greensand, and vol. ii. (in press), by the same author, for the divisions of the Chalk. The two first-mentioned memoirs contain full bibliographies of works on the geology of Surrey up to the date of their publication ; and it has therefore not been deemed necessary to give such references in the present sketch. References to some later papers will be found in footnotes to subsequent pages, but for a fuller list the reader should refer to the account of the bibliography for the period 1889 to 1899 contained in Mr. W. Whitaker's presidential address for 1900 to the Croydon Microscopical and Natural History Club (Proceedings 1900, pp. iii.-xvii.). The numerous reports of excursions in Surrey in Proceedings of the Geologists' Association should also be consulted, as these contain lists of references, besides frequently record- ing new observations. The greater part of the county lies within Sheet 8 (old series) of the Geological Survey map, on the scale of one-inch = one mile ; but it also enters Sheets 6, 7 and 9 of the same map.