2 On Drift. 



this subject the leading one of my address. In doing so I shall 

 not restrict myself to a mere analysis of the communications which 

 have been made to us. I shall venture to criticise them with such 

 freedom as may, I trust, require no further apology than that 

 which the desire of advancing our science may afford. I shall 

 also, before I enter on this more detailed analysis, endeavour to 

 bring before you a general view of some of the more important 

 parts of the subject, under the aspect which it now presents to us. 

 Papers also on other subjects have been brought before us, which 

 are far too important to be omitted in any general review of our 

 proceedings, and to which I shall in the sequel direct your atten- 

 tion. 



I. Drift. 



If the period of the drift involved only a repetition of the action 

 of those geological causes which we recognise in earlier geological 

 periods, it would still have an especial interest, as approximating 

 to our own times, and as less likely than those earlier periods to 

 have the nature and character of its operations and phenomena 

 masked by those of succeeding periods. But besides this, we have 

 reason to regard it as a period of peculiar conditions, and of phe- 

 nomena referable to peculiar causes, the study of which has opened 

 to us entirely new views respecting the agencies which have so 

 marvellously modified the face of our planet, by the continual 

 transference of matter from one part of its surface to another. 

 The study of this period has also led us to a knowledge of climatal 

 conditions not before suspected, and to various researches into the 

 causes which may have produced those conditions ; and thus we 

 have extended our knowledge of one of the most interesting branches 

 of terrestrial physics. 



There is perhaps no branch in which speculative geology has 

 recently made more satisfactory progress than in theoretical views 

 respecting the agencies by which the larger masses associated with 

 the drift, the erratic blocks, have been transported from one loca- 

 lity to another. At the same time, no subject, perhaps, has been 

 more characterised, in passing through its various phases, by ex- 

 treme hypotheses and premature conclusions. When water alone 

 was recognised as the means of transport, hypotheses were some- 

 times made respecting the magnitudes of single waves, and their 

 passage even over elevated mountains, which nearly all of us should 

 now agree in condemning as extravagant ; and effects were attri- 

 buted to them which, from the transitory character of any single 

 wave, were not only improbable, but perhaps physically impos- 

 sible. In the abandonment of such extreme hypotheses we have 

 made a most salutary step. Nor was the introduction of the 

 glacial theories of transport, by glaciers and floating ice, unattended 

 by hypotheses, which might be deemed extreme hypotheses with 



