MODERN FORMATION. 



ages long gone by, for in certain modern formations, which con- 

 tinue to be formed under our eyes, we find human skeletons im- 

 bedded in the substance of the rock, and already presenting the 

 characters of fossils of the tertiary period. One of the most re- 

 markable examples of this kind has been discovered in the island 

 of Guadaloupe. 



Thus far we have presented a sketch of the earth's structure as 

 revealed to us by an examination of its crust, only in reference, 

 however, to the order of superposition of its formations, resulting 

 from great geological convulsions, and characterized by the remains 

 of animals found entombed in it. When we reflect on the incon- 

 ceivable length of time it has evidently required to effect all these 

 changes, anid elevate one above another gigantic stories of various 

 rocks, the imagination is startled ; when we see entire creations of 

 plants and animals covering the surface of the earth, and inhabit- 

 ing the waters, disappear after a time, leaving a few mutilated re- 

 mains as the only irace of their existence, and give place to a new 

 flora and a new population ' of animated creatures, destined to un- 

 dergo in turn a similar fate, we are struck with astonishment, and 

 overcome by admiration of the power of the Creator of things so 

 grand and so beautiful. 



LESSON VI. 



INFLUENCE OF INTERNAL AGENTS ON THE SURFACE OF THE EARTH. 



EARTHQUAKES Description Effects of Changes of level pro- 

 duced by Upheaval and Subsidence Constant level of seas 

 Slow and progressive Subsidence General conclusions. 



VOLCANIC PHENOMENA. Explosion Eruption Island of Saint 

 George' Monte-Nuovo Jorullo Vesuvius Definition of a 

 Volcano Submarine Eruptions Volcan of Unalaska Crater 

 of elevation Formation of Craters Effects of upheaval 

 Form of Volcanic Islands Periods in the formation of a 

 Volcano Interior of Craters Kirauea So/fataras Volcanic 

 Joshes Lava Currents Characters of Lavas Dykes Gas- 

 eous Volcanic Products Eruption of Mud Solid products 

 of Volcanoes Trachyte Obsidian Compact Lavas Po- 

 rous Lavas, fyc. 



1. We have spoken of formations and of their relative order of 

 superposition, and occasionally alluded to the various causes which 

 affect them. From what we have said it might be inferred that 

 the several formations are so many concentric spheres, enveloping 



1. Why is it that the surface of the globe is not entirely smooth, free 

 from mountains and valleys ? 



