34 CONSISTENCY OF GEOLOGICAL 



these vapours may have readmitted light to the earth, upon 

 the first day, whilst the exciting cause of light was still ob- 

 scured ; and the farther purfication of the atmosphere, upon 

 the fourth day may have caused the sun and moon and 

 stars to reappear in the firmament of heaven, to assume 

 their new relations to the newly modified earth, and to the 

 human race.* 



We have evidence of the presence of light during long 

 and distant periods of time, in which the many extinct fossil 

 forms of animal life succeeded one another upon the early 

 surface of the globe : this evidence consists in the petrified 

 remains of eyes of animals, found in geological formations 

 of various ages. In a future chapter I shall show, that the 

 eyes of Trilobites, which are preserved in strata of the tran- 

 sition formation, (PI. 45, Figs. 9, 10, 11,) were constructed 

 in a manner so closely resembling those of existing Crus- 

 tacea ; and that the eyes of Ichthyosauri, in the lias, (PI. 10, 

 Figs. 1,2,) contained an apparatus, so like one in the eyes of 

 many living reptiles and birds, as to leave no doubt that these 

 fossil eyes were optical instruments, calculated to receive, in 

 the same manner, impressions of the same light, which conveys 

 the perception of sight to living animals. This conclusion is 

 farther confirmed by the general fact, that the heads of all 

 fossil fishes and fossil reptiles, in every geological formation, 

 are furnished with cavities for the reception of eyes, and 

 with perforations for the passage of optic nerves, although 

 the cases are rare, in which any part of the eye itself has 

 been preserved. The influence of light is also so necessary 

 to the growth of existing vegetables, that we cannot but 

 infer, that it was equally essential to the development of 

 the numerous fossil species of the vegetable kingdom, which 

 are coextensive and coeval with the remains of fossil ani- 

 mals. 



* Sec Note, p. 30. 



