GREAT CHANGES. 



69 



called " galena," the ore from which all the lead of commerce 

 is obtained ; it is not well known how the veins of this and 

 similar substances got into these crevices, but it is probable 



PIG. 19. PERN (Pecopteris ligata) PROM UPPER SHALE, SCARBOROUGH. 



they were injected in a fluid state by some unequal pressure 

 on the liquid beneath, or deposited by electrical action. 



The great world of vegetation was thus destroyed, giving 

 place to new forms of animal and vegetable life. The 

 temperature, all this while sinking, had reached a degree 

 somewhat resembling the hottest regions of the earth at the 

 present day. The waters had changed their localities, new 

 mountains and new continents had made their appearance, 

 and again did the ever-active waters begin to demolish and 

 wear down the asperities of the surface and deposit the 

 results upon the strata below in the form of the new red 

 sandstone and magnesian limestone, the former containing 

 iron in great abundance, and the latter magnesia (an earth 

 not met with before), both of which substances were probably 

 ejected as volcanic products and afterwards combined with 

 the carbonic acid of the air/ 



During the formation of these strata there appears to have 

 been both birds and quadrupeds of many kinds, together 

 with a reptile much resembling a frog, but of great size, being 



