117 
rally in any rock-salt formation. As sulphate of magnesium 
and chloride of magnesium are constituents of sea- water 
and generally present in all waters flowing from rocks, 
either crystalline or sedimentary, their presence during the 
deposition of rock-salt is ensured, whilst the presence of 
hydrochloric acid would also he possible if a slight rise of 
temperature took place during the deposition, it being a fact 
that magnesium chloride gives off hydrochloric acid during 
evaporation at comparatively low temperatures. 
In the discussion which followed the reading of the above 
paper Mr. Binney, F.B.S., read an extract from Trans. 
Man. Geol. Soc., Yol. I., p. 87, to the following effect, viz. — 
“On the Marine Shells found in the Lancashire Coal 
Fields, by E. W. Binney. 
“ Immediately above the ‘ Bough rock’ at Birtle Dean, 
near Hey wood, is the Featheredge coal, about two feet 
thick ; this seam has a roof of one yard in thickness, con- 
sisting of black shale which is full of the Pecten, Goniatites, 
Povidonia, &c., mixed with various species of Ferns, Lepido- 
dendra, and Sigillarise. It is a singular fact that the black 
shale has scarcely ever been seen on the roof of this coal, 
except at Messrs. Bamsbottom’s colliery, at Birtle Dean. At 
Fecit, within two miles of the last named place, and other 
localities, the roof of the coal consists of a coarse conglomerate 
of quartz pebbles, containing numerous garnets and crystals 
of carbonate of barytes, generally presenting a water-worn 
appearance. I have also observed small pieces of opal im- 
bedded in this rock,” 
