378 Reports and Proceedings. 



near Beeston, where they occtirred of all sizes, from |^ to f an 

 inch on the face of the cube, these specimens showed very decidedly 

 the concave-shaped character of the crystals of chloride of sodium. 

 In a small cutting near Beaumanor Park, pseudomorphs were also 

 found ; these in common with all others found near the edge of 

 Charnwood Forest, are imperfect and irregular. Mr. Plant had 

 searched the Upper Keuper beds on the west side of the river 

 valley near Leicester for pseudomorphs without success ; and gave 

 a description of the rocks, which have a total thickness where fully 

 developed, of about 90 feet. Mr. Plant next discussed the origin of 

 these pseudomorphs. Hugh Strickland was apparently the first to 

 notice them, and considered them to have been the cavities of pre- 

 existing crystals, filled with sand, poured in from above. That the 

 crystals were chloride of sodium and not iron pyrites Mr. Plant 

 considered established by the fact that the time required for the 

 formation and removal of the latter mineral would be too great ; 

 whereas it is evident that the process of formation and removal must 

 have taken place in the interval between the deposition of the lower 

 bed of sand and that of the one immediately above. A sandy marsh, 

 covered by the sea at spring tides would supply the requisite 

 conditions. Between the tides the sea-water covering such a marsh 

 would evaporate and deposit the crystals of salt, which would then 

 be enveloped by the fine sediment, the returning sea- water would 

 again dissolve the crystals, leaving cubical cavities in the mud 

 which contained them, and these cavities would be filled with a 

 fresh deposit of fine sand brought by the tide, whilst the same sand 

 would form a homogeneous stratum immediately above. This 

 explanation, however, will hardly suit those cases in which the casts 

 are formed projecting from the upper surface of the slabs of sand- 

 stone into the green marl above. Perhaps the crystal in such 

 instances may have been formed between the sand and the mud, 

 and when dissolved the soft cast pressed upwards. Mr. Plant 

 alluded to the discovery of pseudomorphs in other parts of England, 

 and in Germany, and America, and mentioned Mr. W. W. Smyth's 

 important observations that the materials of which the casts are 

 constituted vary with the composition of the adjacent rocks. — Mr. 

 Stevenson thought that the formation of pseudomorphs might be 

 going on now, for although there is no salt near Nottingham, yet, in 

 boring, saline springs are met with. — Mr. E. Brown agreed with 

 the author that they were formed at the time of the deposition of the 

 beds, as it would be difficult otherwise to account for the filling up 

 of the hollows with homogeneous matter at a latter period. 



3. Mr. W. Molyneux exhibited an interesting series of organic 

 remains, teeth, scales, and spines of fish, and shells from the Ashby 

 coal field, and gave a short account of them. He enumerated no 

 fewer than 19 genera of fish occurring in the Kilburn coal shales 

 at Bretby. 



4. Mr. H. T. Brown on "The absorption of carbonic acid by 

 metallic copper." The author first called attention to Prof Graham's 

 experiments, which show that certain metals heated to redness in an 



