LESSONS IN GEOLOGY. 381 



raals are able to move their ears freely and many can move por- 

 tions of the skin ; in general, man can move neither the ears nor skin 

 and yet muscles for moving the ears and scalp exist in an aborted 

 form, and occasionally individuals can use them. The presence 

 of these muscles is not explained by special creation, but on the 

 theory of descent with variation they indicate that some ances- 

 tor of man had use for such muscles. 



The embryos of the higher animals in their development simu- 

 late the forms of lower animals; the embryo of the chick shows 

 the gill slit of fishes and the teeth of reptiles, and it is not till 

 quite late in its embryonic life that the human embryo takes on 

 or begins to develop human characteristics. These phenomena, 

 utterly unexplained on one theory, are at least partially elucidated 

 under the other. According to the theory of evolution, the devel- 

 opmental history of the individual appears to be a short recapitu- 

 lation of the course of development of the species. There seems 

 to be a correspondence between the individual development of the 

 higher animals and the progressive advance of organization 

 in the whole animal series. The geological record gives interest- 

 ing evidence in the case; it is necessarily an imperfect record, for, 

 as a rule, only the hard parts of aquatic life would regularly be 

 preserved, and only a small part of the record has been or can be 

 examined. When the crust was first formed, no life of any kind 

 could exist; but as the earth cooled water and other substances 

 were condensed from the atmosphere, and the inter-actions be- 

 tween the atmosphere, water and crust removed impurities from 

 the air and water, and put them away in permanent form, leav- 

 ing the water and air in a. condition favorable for the lower forms 

 of life. And such forms of life appeared in great abundance, as 

 the thick beds of iron ore and graphite in the older rocks are 

 supposed to show. The life must have been of low form, as none 

 other could have existed under the conditions which probably 

 prevailed. As these chemical reactions continued, the plant and 

 animal life also removing impurities, the air and water gradually 

 became fitted for higher and higher types of life. The early forms 

 of life seem to have been flexible and abundant, so that they 



