110 REPORT— 1872. 



l)y denudation of the plastic clay in Sussex, first determined by Sir Roderick Mut- 

 chison in 1850, but more tliorougbly inveslip;ated by Mr. Montague Phillips in 

 1851, who found it to consist of layers of marl and clay, the upper part composed 

 of comminuted marine shells, the clays being of various coloui's, a bed of lignite, 

 4 feet thick, containing- much sulphur, analogous to that found in the Paris and 

 Hampshire tertiary basins. Faint impressions of dicotyledonous trees were also 

 detected upon the clay. Mr. Phillips also discovered a cluster of fossil fruits of an 

 unknown species, intermediate between the Brazilnut and AValnut, with crystals of 

 selenite among tlie clays, and a thui vein of subsulphate of alumina in an outcrop 

 of what he considered the same formation at Preston\'ille. Patches of the lower 

 Tertiaries are to be seen here and there over the whole area of tlie South Downs, 

 whilst scattered over their surface are water-rolled specimens of the breccia form- 

 ing the base of the tertiary deposits at Seaford and Newliaveu, together witli 

 " grey weathers " or druid sandstones ; while within 200 or 300 yards of tlie 

 Eocene strata at Furze Hill, the excavations for draining the town of Brighton 

 revealed the ruins of the plastic clay once lying in situ in that localitj', consisting 

 of clays and sand, breccia of angular flints impregnated vsdth iron, ironstone, gyp- 

 sum, subsulphate and hydrate of alumina, loamy deposits, crystals of selenite, and 

 ferruginous chalk-rubble. The upper portion of this heterogeneous mass consists 

 of a cliocolate or yellowish loam, and in many plr.ce?, where the chalk immediately 

 underlies it, of ironstone or breccia impregnated with iron, in which case the sub- 

 cretaceous strata are in every stage of decomposition. TJie loam contains chalk- 

 like granules, which, on being exposed to atmospheric action, crumble into a fine 

 ochraceous powder. This is probably effected by the percolation of water highly 

 charged with acids derived from the soil, iron, or decomposing iron-pyrites, which, 

 lilce a disease, eats deep down into the core of the chalk, and eventually converts it 

 into the ochraceous tree-bearing loam, such as forms the soil of the ISIontpellier 

 district and of the copse by the roadside to the dyke. The claA's or brickearth, if 

 it be such, the author believes to be of a date anterior to that lying in the Hove 

 Levels. The breccia, in immense masses, lies mingled with the clays and chalk- 

 rubble as if it had been torn from its bed by some mighty force. Hundreds of tons 

 were extracted from an excavation 2 feet 6 inches in width at tlie bottom of Clif- 

 ton Hill at its junction with Montpellier lload up to St. Michael's Place, where 

 it lay piled up like a wall to the height of 5 feet. This interesting section was 

 showed upon the plan which the engineer of the works, Mr. Good, kindly pre^iarcd 

 for the author. Much of this conglomerate has undergone intense chemical action, 

 some specimens being scarcel}' recognizable from " slag." Many of its cores are 

 ornamented with calcites, crystals of selenite, and gaseous botiyoidal bubbles coated 

 with a delicate bloom of violet, yellow, and green. The subsulphate and hydrate 

 of alumina lie in veins and masses imbedded in the claj-s, from a milk-white 

 powdery substance up to the consistence of gypsum. One specimen assumed the 

 form of a trunk of a tree ; its lignite-like coating, on being analyzed by Dr. Flight, 

 of the British Museum, was, however, found to consist of manganese, together with 

 a small proportion of cobalt. Far from being a scarce mineral, the author de- 

 scribed it as being plentifully spread over the chalk-districts wherever ironstone or 

 iron-pyrites was superimposed upon clay. Specimens of the tree-like variety the 

 author had extracted from chalk in which it was completely isolated, the chalk 

 matrix showing no signs of decomposition. He had found portions of clay, too, 

 similarly isolated in chalk-strata with no appearance of rents or fissures ; and the 

 questions were, How got the clay there ? and how was the subsulphate of alumina 

 formed ? 



Mr._ Howell, in describing the Coomlie rock or Elephant-bed, drew attention to 

 the cliffs at Black Rock, consisting of this peculiar deposit superimposed upon an 

 old sea-beach lying from 12 to Is feet in the cliff" above the present one, finer 

 sections for inspection being nowhere visible. Sir Rodericlc Murchison and Mr. 

 God win- Austen state that brickearth is the equivalent of Coombe rock, both being' 

 of the same age ; but the observations of the author during the excavations througk 

 the town of Brighton prove Coomlie rock to be the older deposit^brickearth, when 

 present, everywhere overlying it, in the same manner as Coombe rock overlies tho 

 chalk, The equivalent of Coombe rock; therefore, was not brickearth, but chalk- 



