Abstract
REPORTS.
Third Report on the Sub-Wealden Exploration.—Mr. W. Topley made a statement on this subject, embodying the chief points of the report drawn up by Mr. H. Willett and himself. Up to the year 1872 nothing was known as to the beds which lie below the Wealden strata in the south-east of England. The lowest beds exposed were those on the north and north-west of Battle, long worked for limestone. The age of these beds was doubtful, some geologists correlating them with the Purbecks of Dorsetshire, others regarding them as Wealden but of somewhat exceptional character. In 1872, when the Association met at Brighton, Mr. H. Willett proposed to commence a bore hole in these doubtful strata, with a twofold object: (1) to determine the order, thickness, and character of the Secondary rocks below the Weald; (2) to prove the Palæozoic rocks which were supposed to lie beneath at a depth which could be reached. Judging from what is known of the Secondary strata near Boulogne, and comparing them with those exposed in the middle of England, it was hoped that the Palæozoic rocks would be reached at a depth not greater than 1,700 feet from the surface. In August 1874 the boring had reached a depth of 1,030 feet, and was then delayed in consequence of an accident to the rods. This hole was ultimately abandoned, and a new boring was commenced in February 1875, which has been carried to a depth of 1,812 feet. At this point the work has been stopped, in consequence of great difficulties in keeping the hole clear, and it is not proposed to continue the boring further. From the surface down to 175 feet the strata are shales and impure limestones, with gypsum in the lower part. These beds are referred to Purbecks, and with them are now classed the lowest rocks exposed at the surface, formerly called the “Ashburnham Beds.” From 175 to 257 feet the strata are chiefly sand and sandstones; these are held to represent the Portland Beds. Below 257 feet there is a great series of bituminous shales and clays, with occasional bands of cement stone and sandstone. Kimmeridge Clay fossils extend down to 1,656 feet at least, possibly lower; so that this formation is here at least 1,400 feet thick. The bottom beds of the boring, just reached, are oolitic in structure, and contain bands of hard limestone. To this extent, then, the Secondary rocks have been traversed, and their order and structure ascertained. A discovery of some commercial value has been made, for two companies are in existence to work the gypsum. One of these has been for some time in operation; a shaft has been sunk and the mineral is now being raised. Scarcely less important is the knowledge now attained that no supply of water can be got by deep wells or borings into the Sub-Wealden strata. As regards the Palaeozoic rocks, the boring has not had the success that was anticipated. The Secondary strata have proved too thick, and there is little or no hope of reaching the older rocks here._ A boring is now in progress at Cross Ness by the Metropolitan Board of Works; this will be carried through the gault, and may possibly throw some light on this question.
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The British Association . Nature 12, 461–467 (1875). https://doi.org/10.1038/012461a0
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DOI: https://doi.org/10.1038/012461a0