XXVI PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



by many geologists in the first instance with great reservation. One 

 reason of this reserve was, I imagine, the difficulty of conceiving a 

 change of temperature such as required by those theories, exactly 

 opposite to the changes which the geologist had ever contemplated, 

 a change after the glacial epoch from a lower to a higher tempera- 

 ture. Increased knowledge, however, of the causes affecting climatal 

 conditions have enabled us to remove ia great measure this source of 

 doubt. Another reason for hesitation in accepting these theories 

 was, perhaps, to be found in the incautious manner in which their 

 claims were asserted by some of their first advocates, and the un- 

 limited application which were made of them to account for the phse- 

 nomena of transported materials of all kinds. Whatever truth might 

 belong to the facts adduced in support of these theories, it was clear 

 that much of the reasoning founded upon them was untenable. Over- 

 strained applications, however, of physical theories are almost the 

 necessary consequences of their early reception by minds animated 

 by an ardent zeal for the discovery of new scientific truths ; and per- 

 haps this tendency, in certain stages in the progress of science, may 

 be almost necessary to counteract the hesitation of those whom natu- 

 ral timidity, or possibly severer mental discipline and more accurate 

 physical knowledge, may have rendered too slow in the recognition 

 of the germs of new theories, while supported, perhaps, by little of 

 demonstrative evidence. All doubts, however, as to these theories 

 being founded in truth, whether there might be more or less of ex- 

 aggeration in the advocacy of them, soon gave way before the evi- 

 dence collected by northern voyagers respecting the action of ice- 

 bergs, and that supplied by Agassiz, Charpentier, Forbes, and others, 

 who devoted themselves to the study of the constitution and motion 

 of glaciers. Almost all geologists, I conceive, now agree in the 

 opinion that both floating and terrestrial ice have played their part 

 to a greater or less extent in the transport of erratic blocks. 



The theories of Agassiz and Charpentier as to the causes of glacier 

 motion have been refuted by the exact admeasurements made not only 

 by Prof. Forbes, but by those of Agassiz himself; and the specula- 

 tive views of the latter philosopher on the former extension of gla- 

 ciers over the surface of a large portion of the northern hemisphere 

 are no longer received. But, Gentlemen, geologists would be ungrate- 

 ful, if, while they acknowledge, as we all do, the great value of the 

 researches of our countryman Prof. Forbes on the Alpine glaciers, 

 they should in any degree forget the debt they owe to the distin- 

 guished Swiss naturalist and his countryman, who were the first to 

 point out the effects of glaciers in smoothing and striating rocks, to 

 urge their effectiveness in the transport of blocks, and to indicate 

 phaenomena of a past epoch similar to those of the present time, in 

 such a manner as to command the attention of geologists, and finally 

 to lead to the adoption of our present views respecting the glacial 

 epoch. It is especially to M. Agassiz and his ardour in the pursuit 

 of scientific truth that we owe the first knowledge of this subject in 

 our own country. His visits here, and the personal favour with 

 which he was received among us, gave him frequent opportunities of 



