380 
THE GEOLOGIST 
Although we have given Mr. Hunt's paper only in a slightly condensed form 
and almost in his ovni words, the portions we liave omitted are not by any 
means valueless, but should be read by those who are specially interested in 
this curious subject. We have abstracted sufficient to give the general reader 
a clear notion of the state of investigation up to this point. 
In the " Canadian Journal" for May, 1859, Mr. Hunt has published some ad- 
ditional remarks upon this interesting subject in coniirmation of his view " that 
dolomites have been formed in sea-basins, from which the soluble salts of lime 
have been completely separated, as sulphate or as carbonate by the agency of 
alkaline carbonates, wliich afterwards gave rise to carbonate of magnesia," 
which carbonate "a])pears capable, under certain conditions, of slowly combining 
with carbonate of lime, and forming with it a double carbonate, which is 
dolomite." 
Referring to the Report under review, he says, " I have (there) shown two 
processes by wliich sediments of magnesiaii carbonate may be formed. First, 
by the action of solutions of bi-carbonate of soda on basins of sea-water, which 
precipitate all the lime as carbonate, and then give rise to a soluble bi-carbonate 
of magnesia ; and secondly, the action of bi-carbonate of lime on solutions con- 
taining sulphate of magnesia. I have found that the presence of this salt 
greatly increases the solubility of bi-carbonate of lime in water — bi-carbonate of 
magnesia and sulphate of lime being formed by double decomposition. By 
adding alcohol to such a solution, or by evaporating it at a gentle heat, 
gypsum is deposited, leaving the more soluble bi-carbonate of magnesia in 
solution. 
" In the same way, alcohol separates gypsum from a mixed solution of bi- 
carbonate of lime and sulphate of soda — an alkaline bi-carbonate remaining dis- 
solved. 
" The subsequent evaporation in shallow lakes, or basins, of solutions of bi- 
carbonate of magnesia, formed by either of the above-mentioned processes, must 
give rise to deposits of hydrated carbonate of magnesia more frequently 
mingled with carbonate of lime, supplied by springs containing either bi- 
carbonate of Ume or chloride of calcium. The hydrated carbonate of magnesia, 
at 160 degrees C, and perhaps at a lower temperature, under pressure to pre- 
vent the loss of carboluc acid, is converted into magnesite or anhydi-ous car- 
bonate of magnesia ; but if carbonate of Ume be present, the two combine to 
form a double carbonate, which is dolomite, and may be separated from inter- 
mixed carbonate of Ume by the action of dilute acetic acid, at 32 degrees F., 
which readUy dissolves the latter, but attacks the dolomite more slowly. 
" I have found this union of the two carbonates to take place aUke in the 
presence of earthy and alkaline clilorides, sulphates, and carbonates, at tempe- 
ratures between 130 and 200 degrees centigrade. A portion of the magnesia 
is always, under these conditions, converted into magnesite, and may be par- 
tiaUy separated from the dolomite, by taking advantage of the fact that it is 
less soluble in acetic acid at the temperature of 60 degrees F. than the double 
carbonate. In nature, the combination must take place at the lowest possible 
temperature, and one wliich is probably insufficient to produce the insoluble 
magnesite. This, when once found, I have shown to have no tendency to unite 
with carbonate of lime. 
" The application of these observations to the various conditions in which 
dolomites and magnesites are met with in nature, and especiaUy to their asso- 
ciation with gypsum and anhydrite, is evident." 
Some further interesting remarks are added by Mr. Hunt, in his report, upon 
Fish-manures ; and the volume is concluded by a paper by Lieut. E. D. Ashe on 
the longitude of some of the principal places in Canada, as determined by 
electric telegraph in the years 1856-7. 
