XXVIU PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



such inferences will probably ever remain doubtful, but in others 

 there can be no reasonable grounds for doubt. Most geologists ap- 

 pear now to agree about what may be regarded as the two extreme 

 cases, and admit small rounded pebbles as a proof of long-continued 

 aqueous action, and very large erratics with perfectly unwoven angles 

 as equally indicative of transport by ice. If there be any among us 

 not glaciahsts to this extent, I recommend them to the personal study 

 of these blocks. I well recollect, in my own case, that after resist- 

 ing all verbal arguments in favour of glacial theories, I stood at once 

 convinced under the silent appeal of the Pierre a hot on my visit to 

 that magnificent erratic of the Jura. In almost all the cases inter- 

 mediate to these extremes, I fear we have much yet to reconcile be- 

 fore we come to any unity of opinion. And here. Gentlemen, let us 

 ask ourselves in the spirit of candour, whether one cause of this may 

 not be found in our natural tendency to hold too pertinaciously to 

 preconceived opinions. It will not be denied by any one, I imagine, 

 that it would generally be the necessary consequence of a transitory 

 current driving a mass of drift over a level surface, to spread it out 

 in an approximately equable layer ; while such a result could gene- 

 rally be regarded as only the accidental consequence of transport by 

 floating ice. Such a layer would indicate the latter as a possible mode 

 of deposition, the former as a highly probable one. When the gla- 

 cialist contends for the possible rather than the probable mode, let 

 him examine himself strictly whether he may not be unconsciously 

 under the dominion of preconceived theoretical views. Agam, the 

 polishing of rocks and their striation in definite directions may be 

 generally regarded as the necessary consequences of the passage over 

 them of a large mass of ice, preserving its general direction of mo- 

 tion in defiance of merely local obstacles. Such effects might also be 

 produced by the passage of masses of detritus. The former is a. pro- 

 bable, the latter a possible mode of producing these phsenomena* 

 When the opponent of the glacialist, therefore, urges the latter against 

 the former mode of action (except under some particular condition), 

 let him also institute a self-examination as to whether he is exercising 

 his unclouded and unprejudiced judgment. Gentlemen, I would ex- 

 hort you earnestly to prosecute your researches and speculations with 

 a fair and liberal feeling towards the views of others, and especially 

 with an unflinching obedience to the laws of inductive philosophy. 

 Every geologist, who takes an impartial review of the history of his 

 own mind with reference to geological opinions, will probably feel 

 that what is termed consistency of opinion would frequently have 

 been in his own case persistency in error. I feel the more entitled 

 to make these remarks, from the consciousness of having resigned 

 much of my own early convictions respecting the glacial theory ; and 

 I make them in immediate connexion with the subject before us, 

 because I believe that much remains to be done in these superficial 

 deposits before we can completely interpret them ; and I believe also 

 that for our progress towards sound opinion and unity of view respect- 

 ing them, ability and fidelity in the observer will scarcely be more 

 necessary than that fairness and candour without which he will 



