18 ORIGIN OF ROCK-SALT. 
matter in suspension, found its way there, which material, as soon 
as it mingled with the sea-water, would fall to the bottom and 
become a marl. The clay would be deposited at once on 
reaching the salt-water, and this would go on for ages, during 
which time no salt would be formed, while a continuous growth 
of marl would be going on. The existence of these marl beds 
beneath the rock-salt can, in this way, and consistently with 
known laws, be accounted for. ; 
Again, we should expect to find the marl deposits occupying 
a far wider area than the salt which it underlies, which is 
precisely what we do find; and it ought to be so if our theory be 
correct. Marl would be deposited from the very beginning of 
the lake’s existence. Salt would not form until the lake had 
reduced its volume by ~ths. I am aware that I am here in 
conflict with many geologists, who generally manage for the sea 
‘to flow into a depressed area of land, and form a lake, and the 
sun to dry up the water. In this way you may get salt, but 
where is the marl ? 
To complete the story of the origin of rock-salt, I propose now 
to review the physical state of things, hereabouts, in Triassic 
timos, more particularly in reference to the formation of rock- 
salt. I shall confine my remarks to what we may suppose to 
have occurred in the locality of the Cheshire basin, leaving 
out of the question the existence of similar lakes in other 
parts of the Trias aroa. 
First of all we have evidence of the existence of a considerable 
hollow or depression, on the site of the present salt districts, 
now filled up with material of Trias date. The present thickness 
of these salt and marl beds is a thousand feet at the least; this 
only partly indicates the depth of this hollow, which, when first 
cut off from the sea, would necessarily be salt-water, and by sub- 
sequent evaporation, its waters would become more salt, until 
in time it became, from the preponderance of salt, a salt-lake. 
What have we now to replenish this lake with from time to 
time ? A body of sea-water alone, undergoing evaporation, 
would not supply all the necessary elements in the case. There 
