5 



THE POPULAR SCIENCE MONTHLY. 



You are, doubtless, all aware that the crust of the earth, the su- 

 perficial part of the earth, is not of an homogeneous character, but 

 that it is made up of a number of beds or strata, the titles or the prin- 

 cipal groups of which are placed upon the accompanying diagram 

 beds of sand, beds of stone, beds of clay, of slate, and of various 

 other materials. 



On further examination, it is found that these beds of solid mate- 

 rial are of exactly the same nature as these which are at present being 

 formed under known conditions at the surface of the earth ; that the 

 chalk, for example, which forms a great part of the Cretaceous forma- 

 tion in some parts of the world, is identical in its physical and chemi- 

 cal characters, or practically so, with a substance which is now being 

 formed at the bottom of the Atlantic Ocean, and covers an enormous 

 area ; that other bodies of rock are comparable with the sands which 

 are being formed upon sea-shores, packed together, and so on. Thus it 

 comes to be certain that, omitting rocks of igneous origin, all these beds 

 of stone, of which a total of not less than seventy thousand feet is 

 known, have been deposited and formed by natural agencies, either 

 out of the waste and washing of the dry land, or else as the product 

 of plants and animals. Now, these rocks or strata are full of the 

 remains of animals and plants. Countless thousands of species of 

 animals and plants, as perfectly recognizable as those which you meet 

 with in museums at the present day, or as the shells and remains 

 which you pick up upon the beach countless thousands of spe- 

 cies of these creatures have been imbedded in the sand or mud, or 

 limestone, just as they are being imbedded now. They furnish us 

 with a record, the general nature of which cannot be subject to any 

 misinterpretation, as to the kind of things that have lived upon the 

 surface of the earth during the time that is registered by this great 

 thickness of stratified rock. The most superficial study of these re- 

 mains shows us that the animals and plants which live at the present 

 time have had only a temporary duration ; that you will find them 

 and such as they are now, for the most part, only in those uppermost 

 of the strata called Tertiary. As you go back in time their places are 

 taken by other forms as numerous and diversified, but different, and 

 you will find yet others different from the Cretaceous or Tertiary, and 

 from those of the present day, and so on, as you go further and further 

 back. Thus, the circumstantial evidence absolutely negatives the 

 conception of the eternity of the present condition of things. We 

 can say with certainty that such has not been the coui*se of Nature. 

 We can say with certainty that the present condition of things has 

 existed for a comparatively short period ; and that, so far as animal 

 and vegetable nature are concerned, it has been preceded by a differ- 

 ent condition of things. We can pursue this evidence until we reach 

 the lowest of stratified rocks, in which we lose the indications of life 

 altogether. The hypothesis of the eternity of the present condition 

 of things may, therefore, be put out of court. 



