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British Association for the Advancement of Science. 269 
Other experiments, bearing upon this subject, were also detailed, 
which it is unnecessary to mention. They with those already noti- 
ced, were considered interesting in explaining the cause of the de- 
positions of metals in veins; for, as the magnetic theory of Arago, Am- 
pere, and others, requires that free currents of electric matter should 
be perpetually circulating around our earth ina direction at right 
angles to the magnetic meridian, so these currents, instead of merely 
causing the evolution of magnetic phenomena, are shown to be suf- 
ficient to produce most important chemical changes, causing, by 
their passage through masses of clay or earthy matter, the reduction 
and crystallization of the metals diffused through them in solution. 
To one circumstance, Mr. Bird particularly called the attention of 
the meeting, viz. the danger of considering the chemical changes 
produced in the bowels of the earth as in the first place depending 
upon metallic veins themselves ; for, although it was evident that by 
the action of heat upon them, thermo-electric currents may be, and 
no doubt are, developed, yet we must regard the first physical cause 
which induced the deposition and formation of these very veins ; 
and this cause, it is evident, can be none other than, in the first in- 
stance, chemical action. Upon this point, Mr. Bird’s experiments, 
in conjunction with those of Dr. Faraday and M. De la Rive, are 
certainly interesting, as throwing light upon that most obscure of 
subjects, the formation of metallic veins in the bowels of the earth. 
A valuable part of this communication appeared to us to be, that 
in which Mr. Bird suggested that the silification of wood is an elec- 
trical phenomenon. He has undertaken experiments to test this 
theory, and we are happy that so interesting a subject of i ay 
should be in such competent hands. 
Sediment.—The proportion of insoluble matter contained in the 
Mersey, amounts to twenty cubic inches in the flood, and thirty three 
inches in the ebb, in each cubic yard of water; evincing a prepon- 
derance of one in eight in the matter of the ebb, or 48.065 cubic 
yards of silt, &c. which is detained by the banks outside the Rock 
Narrows each tide, with the exception of what the succeeding ebb 
disturbs, at the exhausted stage of the former ebb. Thus, the 
ebb of to-day ranges over sixty four square miles, and the next 
ebb over forty four square miles, reducing by one third the first 
day’s layer, that being the relative proportion of silt held in so- 
lution, and deposited over the outer area, at the northern margin 
of which the cross set of the Irish Channel ebbs, limits the deposit 
Vou. XX XIITI—No. 2. 3D 
