S. G. Perceval — Occurrence of " Websterite" at Brighton. 121 



VI. — On the Occukrence of Webstebite at Brighton. 



By S. G. Pekceval, F.G.S. 



ON the 30th. July last year I observed that a deposit of Websterite, 

 subsulphate of alumina, had been cut into, in excavating for 

 the new system of drainage in the Montpelier Eoad opposite the 

 south end of Vernon Terrace. It occurs at a depth of 16 feet from 

 the surface of the road, beneath a ferruginous deposit of varying 

 depth, which overlies the chalk on the summit of the hill, consisting 

 of ochreous clay with occasional flint-breccia and masses of hematite ^ 

 iron ore in some instances mammillated and associated with crystals 

 of selenite. The iron ore is occasionally friable and of a cindery 

 appearance, containing in its cavities angular pieces of chalk and 

 occasional groups of crystals of selenite. The deposit of Websterite 

 is about three feet wide at its junction with the overlying ferru- 

 ginous mass, narrowing as it descends, apparently occupying a fissure 

 in the chalk, which has at some time been filled with clay, or 

 has been formed by some decomposing action on the chalk, the 

 chalk intruding occasionally into the vein of Websterite. The 

 mineral varies much in colour and appearance, consisting in some 

 places of a soft white powder, which, I am informed by Sir W. C 

 Trevelyan, he has observed in specimens at Newhaven, and which 

 he has ascertained by the microscope to consist entirely of minute 

 transparent crystals, the nature of which he believes has not yet 

 been investigated ; sometimes in masses of various size presenting 

 the appearance of meerschaum, compact and structureless, or some- 

 what botryoidal in form, occasionally presenting a concentric struc- 

 ture, and rarely and only in a certain portion of the deposit exhibit- 

 ing spherical concretions with a radiating structure. Specimens of 

 these various forms I have presented to the British Museum. A 

 mass of yellow clay with imbedded chalk fluits divides the summit 

 of the vein of Websterite, and near the clay the mineral assumes the 

 character of allophane, having a yellow ivory-like appearance, to- 

 wards the chalk forming the wall of the vein of Websterite. The 

 wall of the vein is marked by a dark line caused by the association 

 of a soft black substance, oxide of manganese, with the Websterite. 



The deposit of Websterite which was exposed in the Montpelier 

 Eoad was again met with at about the same depth in Clifton Hill, 

 near its junction with the former. Here the mineral was associated 

 with a hard white breccia apparently composed of a mixture of sub- 

 sulphate of alumina, with gypsum, and with occasional imbedded 

 chalk flints. The haematite or manganese was also developed in 

 connexion with this formation. 



A deposit of Websterite has also been met with opposite Powis 

 Villas, at no great depth in the chalk, consisting of a horizontal 

 layer about a foot thick, differing much in appearance from that in 

 the Montpelier Eoad, having apparently been more uniformly crystal- 

 lized and of a less heterogeneous character than the former, con- 



1 Limonite ? Edit. Geol. Mag. 



