6 PALEONTOLOGY OF KENTUCKY. 



Vast as the geological field appears, and in reality is, it, nevertheless, forms 

 only a small portion of the whole contents of our globe. The deepest excava- 

 tions rarely extend to a depth of 2,000 feet below the level of the sea, though 

 their absolute depth may be greatly in excess of this, inasmuch as most of 

 them ar< in mountainous regions. The bending of the strata very often gives 

 us an insight into greater depths, but even this amounts only to a few miles, 

 and forms only a small portion of the earth's radius. Beyond these depths 

 geology is barred, as far as actual observations are concerned, but its inquiries 

 may penetrate deeper ; it may speculate about the nature and condition of the 

 earth's interior. About this matter different theories have been advanced, but 

 as all of them are based on mere speculation, none have met with a general 

 acceptance by the scientific world. Whether the center of our globe is solid 

 or fluid, whether it is a vacuum or filled with compressed air, we are unable 

 to decide with certainty. Some facts speak for a solid and others for a fluid 

 center, and still others can not be accounted for by either condition. 



Some European scientists, like Leslie and Halley, consider the earth a hollow 

 sphere, which, according to Leslie, was filled with imponderable material, pos- 

 sessing an enormous repulsive force. These philosophic speculations of savants 

 were taken up by Captain Symmes, of Kentucky, who, by adding his own 

 fantastic dreams, enlarged them to the so-called "Symmes' Theory." Symmes 

 insists that the interior of our globe is not only hollow, but that it is also 

 inhabited by animals and plants ; that it possesses a very mild climate, and is 

 illuminated by two planets, which he calls Pluto and Proserpina. He felt 

 so convinced of the existence of his subterranean country, that he repeat- 

 edly extended private and public invitations to Alexander von Humboldt, Sir 

 Humphrey Davy, and other celebrated scientists of this country, and of the 

 old world, to accompany "him on his intended subterranean expedition. 



ROCKS. 



The solid portion of the earth is composed of different materials or rocks. 

 The term "rock," as commonly understood, signifies a hard and stony mass, 

 such as granite, quartz or limestone, but in its geological meaning, it embraces 

 all solid constituents of our globe, the hard and stony, as well as the soft and 

 incoherent matter ; thus, loose sand and soft clay are just as well included in 

 that term as basalt and quarrystone. Before geology enlightened the people, 

 it was the general belief that all the rocks, with their present form and arrange- 

 ment, were thus created. This belief, though still adhered to by the ignorant 

 masses, and by bigots, has disappeared from the minds of all who ever came 

 under the influence of geological reasoning. Geology informs us, that all the 

 rocks in their present structure, composition and arrangement, are the pro- 

 ducts and results of many different conditions under which our earth existed, 



