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 A HISTORY OF SURREY We shall notice that in these borings the older rocks are much closer to the surface than they would have been if the whole sequence which we found in crossing the county from south to north had been continuous underground up to the places where the borings were made. The various divisions of the Eocene, with the Chalk, the Upper Greensand and the Gault, are indeed fairly represented ; but the great mass of the Lower Greensand is absent altogether at Streatham, and if present at Richmond (respecting which there is much doubt) has dwindled to a thickness of only i o feet ; while the Wealden Series is entirely unrepresented in either section. Furthermore, although the Jurassic rocks at their outcrop in the middle and the west of England constitute a great and varied system rivaling the Cretaceous in extent, and have likewise been proved by deep borings in Kent and Sussex to attain a considerable development beneath the Cretaceous rocks in certain parts of those counties, they are most scantily represented in these sections, only one division of the Middle Jurassic having been recognized therein. If, however, the bor- ings had been made in the southern part of Surrey instead of in the north, it is almost certain that Jurassic strata of very much greater thick- ness and more varied character would have been encountered. This rapid thinning away northward of the Secondary rocks under- lying the Chalk in the south-east of England is a fact of great economic importance in view of the discovery that among the older rocks brought by this cause within practicable reach of the surface, the Coal Measures are included. The possibility that such might be the case was suggested on theoretical grounds by R. A. C. Godwin-Austen nearly half a century ago, 1 and since that time much has been written on the subject. 2 It was not however until 1890 that the existence of Coal Measures was actually proved, in an experimental boring at the foot of Shakespeare's Cliff at Dover, where they were entered at a depth of 1,157 f eet below the surface, and penetrated for 1,173 ^ eet further and found to contain several coal seams. 3 Several other borings have since been made in Kent, and one of these, at Ropersole eight miles west- north-west of Dover, again reached the Coal Measures, beneath 1,580 feet of Secondary rocks. 4 Meanwhile efforts have been made to sink shafts for the mining of the coal at Dover, but at the time of writing the coal has not actually been reached in the pits. The westerly limits of this concealed coalfield still remain to be proved, and therein lies the importance of the matter in regard to Surrey. ' On the Probable Extension of the Coal Measures beneath the South-eastern part of England,' Quart. Journ. Geol. Soc., vol. xii. p. 38. 8 For references to this literature up to 1889, see Mem. Geol. Survey, f The Geology of London,' vol. i. chaps, ii. and iii. : and for recent review of the subject see W. Whitaker's Presidential Address to the Geological Society, Quart. Journ. Geol. Soc., vol. Ivi. (1900) pp. Ixxi. Ixxxv. 8 See Prof. W. Boyd Dawkins, ' On the History of the Discovery of the South-eastern Coalfield,' Trans. Manchester Geol. Soc., vol. xxv. pt. vi. (1897), containing references to pre- vious publications. 20
 * Prof. W. Boyd Dawkins, Rep. British Assoc. for 1899, p. 735.