46 PROF. EDWARD HULL, LL.D., P.R.S., P.G.S., ON 



occurrence of the known beds of rock salt lend little support 

 to tliis view ; and recent investigations have led to the con- 

 clusion that deposits of rock salt have been accumulated 

 over the floors of inland salt lakes like that of tlie Dead Sea 

 in Palestine, along whose banks such deposits occur in the 

 form of terraces which once formed the bed of the inland 

 lake itself, Avhen at a higher level than at present, but owing 

 to the lowering of its waters are now exposed along its western 

 margin, as in the case of the terraced hill known as Jebel 

 Usdum. Another fatal objection to the view of the marine 

 origin of salt rock is to be found in the fact that this rock 

 generally consists of nearlypure chloride of sodium, while ocean 

 water contains large proportions of the chlorides of calcium, 

 magnesium, and potassium, the precipitation of Avhich would 

 result in a deposit very different from that of the rock salt of 

 Cheshire and Worcestershire, which is composed of 98"30 per 

 cent, of chloride of sodium and only small traces of other salts. 



7 But in addition to the evidence derived from organic forms 

 of the primteval ocean we apparently possess very remark- 

 able direct evidence that the waters were highly saline. It 

 is known that some strata of the Upper Silurian period in 

 North America are saliferous, constituting the Onondaga salt 

 group and the Trenton and Chazy limestone series.* These 

 strata are characterised by large numbers of marine organisms, 

 and there can be no doubt that they were formed in the 

 waters of the Silurian seas. They also yield large quantities 

 of saline waters which are used in commerce, and in which 

 chloride of sodium predominates ; and as the strata are often 

 in the condition of basins below the level of the outer ocean, 

 Dr. Sterry Hunt has inferred that the waters with which they 

 are saturated were originally those of the Palaeozoic ocean 

 in which the strata were deposited. In other cases, however, 

 where the strata are upraised above the ocean level and 

 highly inclined, the same author considers that surface waters 

 have gradually replaced those originally contained in the 

 strata.! Thus we are justified in inferring, not only from 

 organic, but from direct physical evidence, that the waters of 

 the early Silurian oceans were salt. 



8 On examining samples of water taken from the open 



* Dana states that in the State of New York the salt is made from 

 strong bi-ine by sinking wells vaiying from 150 to 340 feet in deiith. It 

 takes from 35 to 45 gallons of this water to make a bushel of salt, whereas 

 it takes 350 gallons of sea water for the same result. 



t Chemical and Geological Essays, p. 104. 



