28 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 19, 



far from the head of Loch Awe, I observed aggregations of large 

 angular blocks and other detritus, having the true character of 

 moraines. 



I am disposed, as I have already intimated, to refer most of the 

 polished and striated surfaces, now found at elevations little above 

 the surface of the sea, to floating or rather half-Jloating ice. It is, 

 at all events, much easier to conceive and account for the existence 

 of ice in this form in many of these localities, than to explain the 

 existence of glaciers extending many miles along nearly horizontal 

 valleys now occupied by the numerous lochs of the district*. It 

 does not follow, however, that although a large quantity of ice may 

 have existed in this form, it should have been the principal agency in 

 conveying the granitic blocks to considerable distances ; nor do I 

 think that observation sanctions the opinion of such having been the 

 case in this region. I have been told that there are blocks of consi- 

 derable magnitude on the banks of the Clyde, but I have never seen 

 any that might not assuredly have been transported there by com- 

 paratively moderate currents of water. As we recede from the im- 

 micdiate sources of the blocks which are found along the shores of 

 Loch Lomond, Loch Long, and Loch Fyne, the blocks decrease 

 rapidly in magnitude, and scarcely ever present that rough and 

 angular appearance which many of them have close to their original 

 sites. In this part of the district, the blocks which are at all remote 

 from their sources appear to me for the most part, although there may 

 be particular exceptions, to have the character of blocks transported 

 by water through the latter part of their course, whatever may have 

 been the mode of transport nearer to the points from which they 

 originally came. On the south side of Loch Etive, the decrease in 

 the size of the blocks as they recede from Ben Cruachan does not 

 appear to me so rapid as in the cases above mentioned, although they 

 decrease and rapidly disappear along the coast to the south of Oban. 

 The best test, however, by which we might determine whether con- 

 siderable masses of floating ice had or had not been the eff*ective 

 agency in transporting blocks down Loch Etive, would be aflbrded by 

 an examination of the opposite coasts of Mull ; for, if such has been 

 the case, it would appear extremely improbable that a considerable 

 number of blocks should not have been conveyed to that island. I 

 regret that bad weather and other causes prevented my making this 

 examination. 



Some geologists seem to have manifested of late an indisposition to 

 admit the agency of currents of water in the transport of erratic 

 blocks. The effectiveness, however, of this agency in the transport 

 of blocks larger than the great majority of those with which we are 



* It is in this manner that I conceive the polished and striated rocks to have 

 been produced in the neighbourhood of Edinburgh and other places in the eastern 

 parts of Scotland. If the ice floated with perfect freedom, it would be very dif- 

 ficult to account for the determinate directions of the striae ; and no rational ex- 

 planation can be given of glaciers moving, in the proper sense of the term, over 

 so flat a region. Half-floating ice, impelled perhaps by incidental currents, ap- 

 pears to me to aflFord the most rational explanation of the phaenomena. The 

 notion is very similar to that frequently advocated by Sir Roderick Murchison. 



