172 
PKOCEEDIXGS OF SOCIETIES. 
Thus it will be seen this subject is one that has occupied a good deal 
of attention, and has called forth the expression of various opinions re¬ 
garding its formation. 
One or two things regarding its possible, if not probable, formation 
have lately suggested themselves to the mind of the writer; and as they 
may, perhaps, throw some light on the subject, he would beg to offer 
them. 
It is argued by many persons that the great paucity of fossil organic 
remains in all magnesian limestone rocks is proof that the carbonate of 
magnesia could not have been deposited contemporaneously with the 
carbonate of lime. [Now, were great abundance of fossil exuviae, or none 
at all, to he met with in these rocks, the circumstance might he claimed 
as pretty conclusive proof in favour of the above argument; hut the fact 
of a few fossils only being occasionally found in them would appear to the 
writer to he strong evidence in support of the two carbonates having been 
deposited at the same time. Carbonate of magnesia may have been held 
in solution in one sea, and carbonate of lime in solution in another, and 
the one may have been conveyed to the other by means of currents, as 
will now be shown. 
Mr. Maury, in his excellent work on the Physical Geography of the 
Sea, fully explains the theory of oceanic currents, their velocity, and 
power of transporting matter from one sea to another. It is difficult, 
he say s, to form an adequate conception of the immense quantities of 
solid matter, in solution, which the current from the Atlantic carries 
into the Mediterranean; and he mentions the circumstance of several 
vessels having been detained in Almira Bay for three months, in conse- 
sequence of the strong currents between that place and Gibraltar, which 
swept them back whenever they tried to get out. 
Now, suppose these currents, which baffled and beat back this fleet 
for so many days, ran no faster than two knots an hour, assuming • its 
depth to be 400 feet only, and its width seven miles, and that it carried 
in with it the average proportion of solid matter ( 3 ^) contained in sea¬ 
water, and admitting these postulates into calculation, it appears that 
salt enough to make no less than eighty-eight cubic miles of solid matter, 
of the density of water, were carried into the Mediterranean in these 
ninety days. Now, unless there were some escape for all this solid 
matter, which has been running into that sea, not for ninety days merely, 
but for ages, it is very clear that the Mediterranean would ere this have 
been a vat of very strong brine, or a bed of cubic crystals. It may be 
laid down as a rule, he goes on to say, that all the currents of the ocean 
owe their origin to difference of specific gravity between the sea-water 
at one place and the sea-water at another; for wherever there is such a 
difference, whether it may be owing to difference of temperature or dif¬ 
ference of saltness, it is a difference that disturbs equilibrium; and cur¬ 
rents are the consequence. The heavier water goes towards the lighter, 
and the lighter whence the heavier comes; for two fluids differing in 
specific gravity, and standing at the same level, can no more balance each 
other than unequal weights in opposite scales. It is immaterial whether 
