GEOLOGY MALM OR TUFA. In the valley of the Kennet there are a few small patches of a calcareous loam. They rest upon peat or alluvium. One patch near Newbury has been described as full of shells of land and freshwater mollusca and caddis-worm cases. Many of them were coated with concretionary carbonate of lime. It is a flood water deposit. In a well already mentioned it was found to be 6 feet thick. 1 GREYWETHERS OR SARSEN STONES The greywethers have long attracted attention. They are de- scribed in Lyson's Magna Britannia as ' those remarkable stones, called by the country people sarsden stones or the greywethers, which are scat- tered over the Downs. They appear to have been removed by some violent concussion of the earth, as they evidently lie on strata to which they do not naturally belong. The greatest number of them are to be seen in a valley near Ashdown Park on a stratum of chalk, others on a bed of clay in the parish of Compton Beauchamp. They are frequently blasted with gunpowder and used for pitching, etc., but are too hard to be worked.' * The ' Blowing Stone ' on the road from Faringdon to Uffington was described by Mr. James Sowerby in a communication to the Linnsean Society on November 7, 1809." Mr. Aveline remarks that around Middle farm, Knighton Bushes, Weathercock Hill and Hone Warren they are plentiful, and he gives the dimensions of a number of stones, the largest measuring 8 feet by 8 1 feet by 5 feet, 9 feet by 5 feet by 2 feet, and 12 feet by 6 feet by i foot. 4 Similar stones occur on the east of the county on Bagshot Heath, etc. These stones are believed to be derived from the Reading and Bagshot Beds and possibly in some cases from the basement bed of the London Clay. They are usually formed of hard, often very hard, sand- stone or quartzite, and sometimes have a somewhat cherty appearance. Their minute structure, according to Professor Judd, varies greatly. Those with saccharoid fracture stand at one end of the series. An example from Camberley in Surrey is wholly made up of sand grains, and much of the cement is ferruginous. At the other end of the series stand sarsens with a fracture like some cherts. He mentions one case where the original sand grains had almost wholly disappeared and an aggregate of grains of secondary quartz had been formed. 6 Mr. Hudleston has described this class of stone as siliceous doggers or concretionary slabs which have hardened in situ and have resisted the atmospheric agencies of destruction, and after noting specimens which 1 Prof. Geol. Assoc. (1879-80), vi. 188 ; see also a paper by A. S. Kennard and B. B. Woodward, op. cit. (1901-2), xvii. 213. 8 Lysons, Magna Britannia (1806), i. 192. s Trans. Lin. Soc. x. 405. 4 'Geology of Parts of Oxford and Berks,' Geol. Survey (1861), p. 47. 6 Geological Mag. (1901), p. i. 23
