ORIGIN OF ROCK-SALT, 17 
together, ranged layer upon layer, salt and marl, or crystal and 
clay,—two bodies of very opposite appearance and character. 
I shall endeavour to account for the presence of the marl beds, 
which I conceive will throw additional light on the origin of 
rock-salt. 
Marl, be it remembered, is but a hardened clay, with an extra 
quantity of saline matter. The circumstance of finding marl 
associated with these salt beds, shews that there were in 
existence older and perhaps similar beds, which at this time 
became denuded and redeposited. How wasthisdone? What 
is the principal, I might almost say the only, agent employed in 
the redistribution of clay? It is water. Here comes in a 
singular fact. All waters do not behave themselves in the same 
way in the presence of clay. Sea-water has little or no affinity 
for it; while river-water intimately combines with it. It is 
true that the union is mechanical, but still so thorough that a 
week is scarcely sufficient for its redeposition. Take the action 
of the River Dee as an illustration. A rainfall, followed by a 
flood, occurs, say in the upper waters, and clay finds its way from 
the soil into the river, until its waters are yellow with it. It 
does not settle, but flows on with the stream down to the mouth 
of the river, where, meeting with the salt-water, it quickly settles, 
and with the silt forms an awkward bar or sand-bank, at the 
junction of the fresh with the salt-water. This can also be 
made the subject of an interesting experiment. Stir an equal 
amount of clay into a glass vessel of ordinary water, and another 
of salt-water, and notice the difference in action; the one quickly 
settles, the other may be days about it; the rule would appear to 
be, the denser the solution the quicker the deposition. Let us 
apply this. Rock-salt has been undoubtedly deposited from the 
waters of a salt-lake, with a river flowing into it, as in the 
case of the Dead Sea. If rivers now bring down clay, why not 
this river flowing into the salt-lake. I can see nothing forced in 
this supposition; on the contrary, the great thickness of these 
marl beds points, not merely to the fact of a river discharging its 
contents into the lake, but that a very muddy river, fall of clayey 
