Mr. Hopkins’s Abstract of his Memoir on Physical Geology. 357 
This large quantity of water suddenly separated from a state 
of combination in which it had been solid, produces, by its 
absorption of caloric of liquidity, the frigorific property. 
The sulphates of zinc and magnesia dissolve in muriatice 
acid, and by cooling or evaporation are obtained unaltered. 
The muriatic acid does not appear to produce any change of 
nature. 
When protosulphate of iron is dissolved in muriatic acid, 
the liquor furnishes by crystallization quantities of unaltered 
sulphate and of chloride of iron. Sometimes the sulphate re- 
tains its common quantity of water of crystallization, but at 
others I have obtained a salt giving by analysis: 
Sulphuric acid 18°7 S = 195 
Protoxide of iron 16°7 Fe = 17°3 
Water and loss 14°6 gH = 13-2 
50°0 50:0 
The crystals were always so aggregated that their form 
could not be accurately determined ; they are transparent, 
harder, and of a much lighter green than ordinary copperas ; 
they are quite permanent, and when dissolved in water give 
sulphate of iron with the ordinary quantity of water. 
The sulphate of alumina crystallizes unaltered from its so- 
lution in muriatic acid, bué in more beautiful plates than from 
water. From the solution of sulphate of nickel or of mer- 
cury in muriatic acid, these salts are deposited by crystalliza- 
tion unchanged. 
23, Lower Gloucester Street, Dublin: March 25, 1836. 
LXVII. An Abstract of a Memoir on Physical Geology ; with 
a further Exposition of certain Points connected with the 
Subject. By W. Horxiys, £sq., M.A., F.G.S., of St. Peter’s 
College, Cambridge. 
[Continued from p. 281, and concluded. ] 
IV. npHE two systems of fissures which I have described 
are those which must be regarded according to this 
theory as primary phenomena, from which, as before stated, 
the secondary phenomena of mineral veins, faults, anticlinal 
lines, &c., must be derived. For this second part of the sub- 
ject, I must refer to the second Section of my Memoir, where 
T have entered in detail into the manner in which these latter 
phienomena may be conceived to be derived from the former. 
The number of phenomena which we are thus enabled to 
account for, as the consequences of a simple cause from which 
