Uniformity in Geological Change 



formed by denudation, but have not varied ma- 

 terially in width or depth since Sicily was first 

 colonized by the Greeks. The limestone, more- 

 over, which is of so late a date in geological 

 chronology, was quarried for building those 

 ancient temples of Girgenti and Syracuse, of 

 which the ruins carry us back to a remote era in 

 human history. If we are lost in conjectures 

 when speculating on the ages required to lift up 

 these formations to the height of several thou- 

 sand feet above the sea, and to excavate the 

 valleys, how much more remote must be the era 

 when the same rocks were gradually formed 

 beneath the waters ! 



The intense cold of the Glacial period pro- 

 foundly affected terrestrial life. Although we 

 have not yet succeeded in detecting proofs of 

 the origin of man antecedently to that epoch, 

 we have yet found evidence that most of the 

 testacea, and not a few of the quadrupeds, which 

 preceded, were of the same species as those which 

 followed the extreme cold. To whatever local 

 disturbances this cold may have given rise in 

 the distribution of species, it seems to have done 

 little in effecting their annihilation. We may 

 conclude therefore, from a survey of the 

 tertiary and modern strata, which constitute 

 a more complete and unbroken series than 

 rocks of older date, that the extinction and 

 creation of species have been and are, the 

 result of a slow and gradual change in the 

 organic world. 



117 



