ANNIVERSARY ADDRESS OF THE PRESIDENT. XXVU 



expounding his views ; and I cannot refrain on this occasion from 

 expressing the delight with which I call to mind the open-hearted 

 hospitalities which he exercised in the deep recesses of the Bernese 

 Alps, and from testifying to the perfect unreserve with which he 

 communicated his views to those alike who favoured or opposed 

 them. 



I have already remarked that water was formerly almost the only 

 recognized agent in the transport of erratic blocks. On the intro- 

 duction of the glacial theory it was superseded, and appeared to he 

 almost forgotten, nor does it still seem to have regained what I con- 

 ceive to be its just claims, in the minds of many geologists. On the 

 abandonment, however, of some of the unreasonable claims of the 

 glacial theories, and the distinct recognition of large portions of drift 

 as subaqueous phsenomena, the importance of currents as agents of 

 transport gained more attention, though there are probably many 

 persons who yet fail to realize in their own minds the enormous power 

 which such currents may possess, even without greater velocities than 

 may be easily allowed them. This power arises from the fact, which 

 I have elsewhere demonstrated, that the moving force of a current, 

 estimated by the weight of a block of any assigned form and mate- 

 rial, increases as the sixth power of the velocity of the current. It 

 is this which accounts for the circumstance that the same atmosphere 

 which in one state of motion constitutes a summer breeze, but just 

 sufficient to move the leaf or the flower, exerts at other times the 

 almost irresistible force of the storm. It is on this account, too, that, 

 reasoning from the power of ordinary currents of two or three miles 

 an hour, we are liable to miscalculate so entirely the force of a rapid 

 current. 



I consider the distinct recognition of these three agencies of trans- 

 port — glaciers, floating ice, and currents — as essential to the final 

 establishment of sound theoretical views on this subject, and the 

 great majority of geologists are probably prepared to recognize them 

 to a greater or less extent. It is equally essential that we should be 

 prepared to assign to each of these agencies its share in the great 

 work of transport according to the characters of the transported ma- 

 terials ; for it is alone by a careful study of these distinctive charac- 

 ters that we can hope to decide by what agent the transport has been 

 effected. On this point there appears to be still much discrepancy of 

 opinion, when the test has to be applied to individual cases. These 

 differences of opinion seem to manifest themselves principally on 

 questions relating to the action of water, either with reference to the 

 form in which currents tend to deposit a general mass of drift, or to 

 their effect in rounding and wearing the individual component parts 

 of it, as compared with the tendency of other modes of transport to 

 produce similar effects. It may be that we have not yet studied these 

 effects as referable to different causes with sufficient care, or that we 

 are still too much influenced individually by preconceived notions ; 

 but it is certain that different persons do draw very different infer- 

 ences as to the mode of transport of a given mass of drift, from the 

 characters which its component materials present. In some cases 



