220 THE PHENOMENA OF DRIFT. 



of the southern also, has, at no distant period, been swept over by 

 water, bearing along the field ice of an arctic or antarctic ocean ; 

 that the ridges and hills of gravel, which we meet every where, 

 have been dropped or crowded along into their present shapes 

 and places by these floating masses of ice ; that these have grated 

 along the surface of our mountains and valleys, and swept down 

 then* salient parts, and left the surfaces smoothed, rounded, and 

 striated. Truly, in such conclusions as these, there is not only 

 novelty, but sublimity. 



In other parts of geology, and of other sciences, we are obliged 

 to stop when we have reached the true dynamics of the subject. 

 And the fact that so many geologists have ventured beyond this 

 into the field of hypothesis, has thrown an air of uncertainty over 

 the whole subject, in the view of those who do not distinguish 

 legitimate conclusion from dreamy hypothesis. No science has 

 suffered so much from this cause as geology ; just because it 

 opens vistas into the arcana of time, too long for human ken to 

 reach their extremity. But it does not make the existence and 

 form of the links of a chain near to us any more uncertain, be- 

 cause that chain reaches so far that some -of its Links are invisible. 



One of the most interesting aspects in which the facts and 

 theories concerning di'ift now present themselves, is the evidence 

 they afford of a rapid approach to unity of opinion among geol- 

 ogists, and of a consolidation of geological principles. This has 

 certainly long been one of the most chaotic parts of the science. 

 But difficulties have given way before accurate examination, and 

 the accumulation of facts ; and already, unless I am mistaken, 

 the proximate origin of drift is determined ; and by cai'efully con- 

 sidering those theories on which there is yet a diversity of opinion, 

 we shall see that they differ but slightly ; and that those differences 

 respect points, which may always remain doubtful ; and which, 

 therefore, geologists may discuss without feeling that any thing 

 important depends upon the decision, and with the most enlarged 

 charity towards those who differ from them. How very different 

 then is the state of this subject to-day, from what it was, when 

 some of us first began to look at bowlders and striae, more than 

 twenty years ago I 



