Testimony of Geology. 65 



CHAPTER VII. 



TESTIMONY OF GEOLOGY. 



It will now be profitable to take a brief glance into geological history 

 and see what that science has to reveal in regard to the relations of ani- 

 mals to their environment and to each other in the past. Two impor- 

 tant questions come up in this connection. One is, has there been time 

 enough in the past history of the earth for the evolution of the higher 

 organic forms, as they are now, from the lower? The other is, do the 

 geological records support the assumption that the lower forms have 

 been succeeded, instead of preceded, by the higher? 



It is generally conceded that the earth was formerly a melted mass, 

 which has now become cool on the outside, but that the crust is as yet 

 only a few miles thick. Since the crust began to form, the watery vapor 

 which composed a part of the earth's mass has become condensed into 

 water and run down into the lowest parts. The parts above water have 

 been constantly exposed to the action of winds and rains, and in some 

 parts to that of frost and ice, and in others to melting heat from the in- 

 side. These agencies have wrought great changes, especially in the 

 erosion of the land and carrying it down to the sea where it has been 

 spread out into strata. The cooling of the crust has been accompanied 

 by changes in its form, due to unequal contractions, so that what has 

 been sea at one time becomes land at another, and vice versa. So, ma- 

 terial which in one age is torn from the land and piled away in the sea, 

 may, in another age, be moved again to another place. The number of 

 alternations between sea and land which have taken place in some parts 

 of the world are very numerous. The crust of the earth is in constant 

 movement, although it is on the whole exceedingly small. It is said 

 there is an earthquake somewhere every day. 



The expression, "everlasting hills," which we sometimes use, indi- 

 cates our sense of the extreme slowness with which the hills are worn 

 down and carried off by various dynamic agencies at work on them. 

 If now we try to realize that these hills ( if stratified ) were made of other 

 hills by a process as slow as that which is now at work, and reflect that 

 this business has been going on long enough to carry away a total thick- 

 ness of hills equal to about twenty miles, if we suppose them all in one 

 place, we shall then begin to have some conception of the ' ( everlasting " 

 length of time. 



The tables on pages 68 and 6 9 are intended to show the relative posi- 

 tion and age of the different formations, together with their organic 



