PERMIAN AGE AND CLOSE OP THE PALJKOZOIC. 167 



be deposited where sea water, which always contains 

 salts of magnesia, is evaporating in limited or circum* 

 scribed areas into which carbonate of lime and carbon-r 

 ate of soda are being carried by streams from the land 

 or springs from below ; * and it is also to be observed 

 that solutions of sulphuric acid, and probably also of 

 sulphate of magnesia, are characteristic products of 

 igneous activity. Hence we find in various geological 

 periods magnesian limestones occurring as a deposit in 

 limited shallow sea basins, and also in connection with 

 volcanic breccias. Now these were obviously the new 

 Permian conditions of what had once been the wide 

 flat areas of the Carboniferous period. Still further^ 

 we find in Europe, as characteristic of this period, 

 beds impregnated with metallic salts, especially of 

 copper. Of this kind are very markedly the copper 

 slates of Thuringia. Such beds are not, any more 

 than magnesian limestones, limited to this age; but 

 they are eminently characteristic of it. To produce 

 them it is required that water should bring forth from 

 the earth's crust large quantities of metallic salts, and 

 that these should come into contact with vegetable 

 matters in limited submerged areas, so that sulphates 

 of the metals should be deoxidized into sulphides. A 

 somewhat different chemical process, as already ex- 

 plained, was very active in the coal period, and was 

 connected with the production of its iron ores ; but, 

 in the Permian, profound and extensive fractures 

 opened up the way to the deep seats of copper and 

 • Funt, " Silliman's Journal," 1859 and lb66. 



