16 ORIGIN OF ROCK-SALT. 
of the rarer forms of salts found in sea-water. Deposits of 
common salt occur at the height of 300 feet above the water, 
and are from 100 to 150 feet in thickness, and extend for five 
miles along the shore. 
Let us see the bearing of these facts upon our subject. In _ 
later geological times, when the Asian continent arose from its 
submergence, it must have enclosed a column of water equal in 
height to the difference between the level of the Mediterranean 
and the lowest depth of the Dead Sea; this would give 2600 ft. 
This sea must have covered a considerable extent of country, 
much of it is still below the Mediterranean. Lake Tiberias, 
60 miles distant from the Dead Sea, is 84 feet below the level. 
This body of water has now all been evaporated, and the patch 
of briny water which now forms the Dead Sea is all that is 
left. An analysis of its waters shows that it has long since 
passed the eleventh hour of its existence, has deposited most 
of its common salt, and represents an accumulation of sea- 
water after parting with 99 per cent. of its substance, and is 
undergoing further concentration. I¢ is, in fact, what is known 
to chemists as a “ Mother liquor,” being made up of salts which 
exist only in an infinitesimal degree in sea-water, but which now 
preponderate to the exclusion of common salt and gypsum, 
which have long since left the water, and are to be seen as 
rock masses extending for miles, and as thick as anything of 
the kind we have in Cheshire. This is apparent to the eye, 
but what of the deposit of marl and salt at the bottom of the 
sea? Who is to estimate its thickness? The probabilities are 
that the salt beds below the surface are far more extensive than 
those above. 
Intimately connected with rock-salt are the well-known marl 
beds. Their presence is a sort of geological puzzle. JuKgs, in 
his Manual, observes ‘The accompaniment of rock-salt with 
the red and variegated clays has not yet been explained. 
When it is, it will probably throw great light on the cir- 
cumstances under which the rock-salt itself has been deposited.” 
The difficulty here is, I imagine, finding rock-salt and marl beds 
