THE DATE OF THE GLACIAL PERIOD. 533 



tation of Lyell's principle of uniformity in Nature's opera- 

 tions. This has led to an exaggerated estimate of everything 

 pertaining to geological time. There is a prevalent popular 

 impression that all geological events happened a great while 

 ago. This impression arises largely from the imperfect ap- 

 prehension of the extent to which changes are now going on 

 in the world. In reality, however, Lyell's greatest service 

 consisted in quickening our conception of the instability of 

 the present condition* of things, and of the intensity of 

 present natural forces. He riveted the attention of his 

 readers upon the cumulative effect of such earthquakes as are 

 now of daily occurrence, and occasionally of enormous influ- 

 ence, and continually reminded them of the frequency and 

 intensity with which new volcanoes are now from time to 

 time bursting forth. Continuity, therefore, rather than uni- 

 formity, is the word which most properly expresses the prin- 

 ciple underlying the theories of this great geologist. A pe- 

 rusal of his works makes it evident that evolution, and not 

 dull repetition, characterizes the processes of Nature. There 

 is therefore really nothing in Lyell's working principle to 

 raise any antecedent presumption in favor of an extreme 

 antiquity for the Glacial period. 



On the contrary, the present tendency, both amoug as- 

 tronomers and geologists, is to diminish estimates of geologi- 

 cal time in almost every period. The hundreds of millions 

 of years claimed, not long ago, as necessary for the deposition 

 and inetamorphism of the geological strata, and for the ele- 

 vating and eroding forces to produce the present contour of 

 the earth's surface, have on geological evidence been reduced 

 to much more moderate limits. Thirty million years is now 

 shown to be ample for the deposition, by forces still in op- 

 eration, of all the sedimentary strata of which we have 

 knowledge. At the same time the astronomers affirm that 

 life can not have existed on the earth earlier than twelve 

 million or fifteen million years ago.* Before that period 



* See Newcomb's "Popular Astronomy," pp. 513-519. 



