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PROCEEDINGS OF THE GEOLOGICAL SOCIETY, 



(c, d, & e) being free from such debris, it is a natural inference that 

 the flint-drift has not passed from the subtending chalk-escarpments. 

 Near Petersfield chalk-flints alone constitute this detritus ; but in 

 moving eastwards to Rogate and Trotton we find that portions of 

 hard ironstone, the clinkers or car-stone of the Lower Greensand, as 

 well as chert of that formation, are added to the mass. In the envi- 

 rons of Trotton, Midhurst, and Petworth, where the formation has 

 expanded, clinkers and chert are indeed near at hand, in situ, from 

 whence the additional materials could have been derived. 



In recently extending my researches eastwards to the district around 

 Pulborough, under the guidance of my friend Mr. Martin, who has 

 so ably illustrated the physical structure and dislocations of the rocks 

 around his residence*, he pointed out to me how the detritus of the 

 Lower Greensand was often arranged in East and West ridges (locally 

 termed £ rigs'), which lie indifferently upon various strata, often in- 

 termixed with angular chalk-flints and some chert. As in the sand- 

 hills near Petersfield and at West Heath and Rogate Common (fig. 3), 

 the detritus around Pulborough is distributed at various altitudes, 

 and is everywhere unstratified. 



In going eastwards from the drainage of the Arun to that of the 

 Adur, the lower grounds occupied by the Weald Clay are seen to rise 

 into eminences on either side of the high-road from Horsham to 

 Worthing, and it is just upon the slopes or summits of these eleva- 

 tions between West Grinstead and Ashington that Mr. Martin pointed 

 out to me irregular heaps of shattered chalk-flints more or less 

 angular, which are mixed up with pieces of the ironstone, or "clinkers," 

 of the Lower Greensand and some chert of that formation. These 

 fragments are disseminated through re-aggregated loam, and here and 

 there they combine to form rocky lumps of " ragstone," or a com- 

 pound breccia. 



It is curious to observe how the chalk-flints, which have been for 

 so many ages deposited upon formations quite foreign to them, have 

 partaken of the colours characterizing those strata. Thus, whilst 

 on the white sands of Trotton Common most of the flints are either 

 white or grey, those which have been long buried amid surface-heaps 

 of ferruginous sand around Petersfield, Rogate, and Pulborough have 

 become ochreous or yellow, whilst some of those which have been 

 arrested in the Wealden clays between Ashington and West Grinstead 

 have passed into various shades of deep red and purple, colours which 

 penetrate the whole mass, and are doubtless due to the modifications 

 produced by the infiltration of water charged with the ores of iron. 



In following this irregular band of drift eastwards until we reach 

 the sea, chalk-flints are found at intervals only upon it ; but in its 

 range from West Grinstead and Ashington on the west, to the district 

 north of East Bourn, it is more specially distinguished by a more or 

 less copious admixture of loam, by which the cold and sterile character 



* One of these memoirs was unluckily mislaid for a long time at the Geological 

 Society, owing to which some good original observations were lost. See Geological 

 Memoir on a part of Western Sussex, 1828, and Observations on the Anticlinal 

 Line of the London and Hampshire Basins, Phil. Mag. 1829. 



