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 GEOLOGY PALAEOZOIC ROCKS The question whether productive Coal Measures are likely to occur at a workable depth beneath Essex is one which has aroused keen interest of late years. So long ago as 1858 a boring at Harwich proved the occurrence of a dark slaty rock beneath the Gault, at a depth of 1,029 ^ eet from the surface. 1 It was then thought that this rock, which was pene- trated to a depth of 69 feet, was of Lower Carboniferous age owing to the supposed occurrence in it of the fossil mollusc Posidonomya. The specimen was however re-examined in 1896 by Prof. W. W. Watts, and he came to the conclusion that, while the rock itself was not at all like that of any known British Carboniferous rock, the supposed fossil was an inorganic structure. 1 A somewhat similar dark slaty rock was touched at a depth of 994 feet in a trial boring in Suffolk, at Stutton on the northern side of the Stour estuary ; and again in a further trial in Essex, at Weeley between Colchester and Walton-on-the-Naze, where the old rock was reached at a depth of 1,094 feet. 8 These two trials in search of Coal Measures were made after due deliberation with the highest geological authorities. That they were unsuccessful is an indication, not that the chances of obtaining coal beneath Essex are hopeless, but that scientific knowledge is insufficient to tell precisely where concealed coal-basins occur. Nevertheless en- terprise need not be damped. There is always a possibility of finding coal where the strata at the surface are newer than the Coal Measures ; but as the older rocks were bent and fractured and largely eroded before the Secondary and Tertiary strata were spread over them, it is evident how speculative must be the search for Coal Measures under these circumstances. Were the exposed coalfields to be covered up with a mantle of Chalk, we should have no certain guide from one successful boring as to the nature of the deep-seated rocks at a distance of a few miles, because there is no regularity in the preservation of coal-basins. Again if rocks much older are proved in a boring, it is quite possible that Coal Measures may exist near by, because in south Staffordshire, Leicestershire and Warwickshire the older Palaeozoic rocks occur in juxtaposition with productive Coal Measures. It has lately been suggested by Prof. W. J. Sollas that Enfield Lock, just across the Lea on the Hertfordshire side, is a likely place for a successful trial. It may be so, but there is no information that would prove that it is a more promising site than any other unproved locality in Essex or Hertfordshire. 4 In Essex several deep borings have been made in search of water. Thus at Wickham Bishop a boring was carried to a depth of 1,180 feet, 1 Prestwich, Quart. Journ. Geol. Sot., vol. xiv. p. 252. 4 For further information on the underground rocks see Whitaker, Geology of LenJen, vol. i. p. 10. (In this work full references are made to the suggestions of Godwin-Austen, Prestwich and others on the older deep-seated rocks.) 3
 * Ann. Report of Geol. Survey for 1896, p. 5. Whitaker, Ref. Brit. Ante, for 1895.