112 On Fossil- Shells. 
but a small excess of eitherof these. The formation of superoxide 
of copper requires another precaution: the deutoxide of copper 
must be put to the oxygenated muriatic acid insuch portions that 
the acid shall be always in excess ; for if the oxide predominate, 
the greater part of the oxygen will be disengaged. In-every case 
‘the oxide is precipitated in a gelatinous mass, er in the state of 
a hydrate: thatof zinc is yellowish,—of copper, olive-green,— 
of nickel, a dirty-looking dark apple-green. The two former al- 
low a portion of their oxygen to be liberated at the common tem- 
~perature. When boiled in water the liberation of oxygen is still 
more abundant ; but they still retain (especially the superoxide 
of zinc) a portion of the oxygen which they had absorbed ; -for 
if dissolved afterwards in muriatic acid, and heat be applied, a 
new quantity of gas is given off. ‘The oxide of nickel is'likewise 
‘decomposed at the boiling temperature ; and even below that 
point its decomposition commences. Treated with muriatic acid 
it dissolves, like the oxides of zinc and copper, and is deoxyge- 
trated by heat without giving off chlorine. These different oxy- 
genated hydrates recover the colours which characterize the com- 
“mon oxides after they have been boiled in water: thus the hydrate 
of zinc passes from yellow to white,—of copper, from olive-green 
‘to dark-brown. It had already been observed by M. Rothoff, a 
Swedish chemist, that the deutoxide of nickel is decomposed by 
desiccation.—These new hydrates, as we see, resemble those of 
barytes, strontian and lime, and form aclass analogous to that of 
‘the oxygenized acids.—1 expect to discover some more of them. 
XIX. On the Importance of knowing and accurately disorimi- 
nating Fossit-SHELts,as the means of identifying particulpr 
Beds of the Strata, in which they are inclosed : with a.List 
of 279 Species or Varieties of Shells, of which the. several 
Stratigraphical. and Geographical Localities are mentioned, 
which seem to require the particular and minute attention of 
the Collectors and. Examiners of Fossil Shells intheir-natural 
Deposits. By Mr..Joun Farry Sen..Mineral Surveyor. 
To Mr. Tilloch. 
‘sir,Ow taking a review of the many particulars regarding the 
Fossil Shells: and ‘other organic remains-of’ Britain, which were 
“published by Edward Lhwyd (or Luid) in 1669, by Dr. Plot in 
1686, by Dr. Woodward in 1729, by G. Brander in 17665 by 
‘Da Costa in 1776,and by John: Walcott, Rev. David Ure, and 
others’ prior to the time when Mr. William Smith began his in- 
vestigations of the Strata of England, about 1792 ; it cannot fail 
of exciting surprise, that these learned and ingenious Writers, and 
the 
