Vol. 56.] ANNIVERSARY ADDRESS OF THE PRESIDENT. lxXXU 



At Streatham and Crossness it is the same, though the borings there 

 are respectively only 14 and 18 miles from that outcrop. The like 

 statement holds good too of Chatham, where the deep boring at the 

 dockyard is about 13 miles from the main outcrop, but only about 

 8 from that of the Maidstone inlier. 



In all the more northerly borings these beds are absent : indeed, 

 so far as we know, it is only in East Kent that they reach to 

 any great distance under the Chalk tract and are then but thinly 

 represented, less than 250 feet at Ottinge (some 5 miles from the 

 outcrop), only 55 at Eopersole, and 94 at the Dover Colliery. 



At Hothfield, in the Lower Greens and tract west of Ashford, the 

 thickness seems to be only about 600 feet ; and at Brabourne, on the 

 Gault east of the same town, about 200 less. 



One fact, therefore, to be clearly learnt from the deep borings 

 in Surrey and in Kent, is the rapid northerly thinning of the very 

 thick Wealden-Purbeck Series. 



The Jurassic Beds. 



Up to this point formations that occur at the surface in the 

 South-east of England, th e district with which we are specially con- 

 cerned, have been dealt with. We may now pass to beds not seen 

 in that district. 



Before any of the deep borings were made nothing was known as to 

 what formations occurred beneath the Purbeck Beds of the Wealden 

 tract, and these were the oldest known beds in the district. The 

 great experimental boring of the Sub-Wealden Exploration, in the 

 parish of Mountfleld, near Battle, carried on the downward series 

 in Eastern Sussex continuously through the Upper Jurassic, in great 

 thickness, and well into the Middle Jurassic, ending in Oxford Clay 

 at a depth of more than 1900 feet. 



For some time this remained the only evidence of Jurassic beds 

 underground within a great distance, the earlier borings at Kentish 

 Town and at Harwich having proved the absence of such beds far 

 off north-west and north-north-east ; but further evidence is now 

 available. 



As regards the Upper Jurassic division, the westernmost occur- 

 rence is at Penshurst, where the boring ends in Kimeridge Clay of 

 considerable thickness at the depth of 1867 feet. The most northerly 

 evidence is at Ropersole, where there may be 10 feet of that clay, 

 between Purbeck Beds and Corallian. The Pluckley boring ends, as 



