ta GEOLOGY AND HISTORY 



this interval the two records must have run more or 

 less parallel to each other, and must be in contact 

 along the whole line. 



The geologist, ascending from the oldest and 

 lowest portions of the earth's crust, and dealing for 

 millions of years with physical forces and the in- 

 stinctive powers of animals alone, at length as he 

 approaches the surface finds himself in contact with 

 an entirely new agency, the free-will and conscious 

 action of man. It is true that at first the effects of 

 these are small, and the time in which they have been 

 -active is insignificant in comparison with that occu- 

 previous geological ages ; but they introduce 



r tjuestrohs 'which constantly grow in importance, 

 down to those later times in which human agency 

 has so profoundly affected the surface of the earth 

 and its living inhabitants. Finally, the geologist is 

 obliged to have recourse to human observation and 

 testimony for his information respecting those modern 

 causes to which he has to appeal for the explanation 

 of former changes, and has to adduce effects produced 

 by human agency in illustration of, or in contrast 

 with, mutations in the pre-human periods. 



The historian, on the other hand, finds, as he 

 passes backward into earlier ages, documentary 

 evidence failing him, and much of what he can obtain 

 becoming mythical, vague or uncertain, or difficult of 

 explanation by modern analogies, until at length he 

 is fain to have recourse to the pick-axe and spade, 

 and to endeavour to disinter from the earth the 



