142 



THE ULTIMATE SOURCE 



and by isolated crystals found scattered through the mass. 

 Rock salt is stratified. It occurs in beds, varying from a 

 few inches to 1,200 feet, and more, in thickness. In the Mayo 

 salt mine, the whole formation is calculated to be 600 feet 

 thick, composed of strata, each of which is supposed to repre- 

 sent one year's deposit. These strata vary in thickness fiom 

 6 inches to 20 feet, and are separated from each other by 

 clay beds, red gypserous, and violet, marls. It is found that 

 the salt is purest, and least stained, in the middle of the seam. 

 Gypsum be<ls overlie the salt beds. In Cheshire, the rock salt is 

 found in horizontal strata, separated by beds of clay and 

 gypsum. Salt crystals are found infiltrated through some of 

 the clay beds. In Wiirtemberg, the salt is enclosed in seams 

 of shell limestone. At Ischl, in Upper Austria, it occurs in 

 horizontal bands, running through the mountains overlooking 

 the town. These mountains are composed of bands of lime- 

 stone and rather impure rock salt, separated from each other 

 by colored gypserous marls. The limestone above the salt 

 is scarcely distinguishable in structure or fossils (Oolitic) from 

 that below it. 



In general outline, beds of rock salt are seldom of uniform 

 thickness ; they are thickest about the centre of the deposit, 

 and thin out towards the circumference, having a lenticular 

 formation. They are often linked together, forming chains, 

 and, when so connected, lie in about the same horizontal plane 



The salts associated with rock salt are precisely those which 

 are formed in association with it in the manufacture of 

 common salt, as gypsum, sodic and magnesic sulphate, potassic 

 and magnesic chloride, &c. 



"We have now before us, as many of the ascertained 

 properties and relations of rock salt, as will be useful in 

 guiding us to form an opinion of its origin. It will not 

 have escaped notice that most of these mark it as a 

 sedimentary rock of aqueous origin. I will now proceed to 



