1851.] HOPKINS ERRATIC BLOCKS OF THE S. HIGHLANDS. 25 



not discover any on the eastern shore within a distance of six or eight 

 miles of the head of the loch. My examination did not extend further 

 to the south. 



3. On the general Configuration and relative Depression of the 

 District at the period of the Drift. 



The two granitic centres of Ben Nime and Ben Cruachan are un- 

 doubtedly those from which the granitic blocks in general in the 

 southern portion of the Highlands have been derived. The particular 

 courses which these blocks have followed bear no constant relation 

 to the points of the compass. On the contrary, we find them 

 radiating from separate centres, each line of dispersion being deter- 

 mined by a configuration of the surface of the country very similar 

 to that now existing. The reason why there are no lines of disper- 

 sion towards the north in the above cases is found in the absence of 

 any valley descending in that direction from the granitic centres. 

 This leads us, and 1 think necessarily, to the conclusion that the 

 general configuration of the district was nearly the same at the time 

 of the dispersion of the blocks as at the present time ; a conclusion, 

 however, which does not by any means invalidate the suppositions 

 that the position of the surface of the land may have undergone 

 great changes with reference to the sea-level, and that the valleys 

 may have been materially modified by denudation, during the period 

 of submergence. There is, in fact, indubitable evidence in different 

 parts of Scotland of the superficial configuration of the rocks older 

 than the Old Red Sandstone having been determined previous to the 

 breaking up of that formation ; for the Old Red Conglomerates 

 occupy entirely or partially valleys which must have existed previously 

 to their dispersion. Some of these valleys also afford most striking 

 instances of subsequent modifications produced by denudation. The 

 valley, now occupied by the sea, between the island of Kerrara and 

 the main-land near Oban, is an instance of this kind. It was obviously 

 filled up by the Old Red Conglomerate to the depth of perhaps 

 several hundred feet ; but the greater part of this mass has been 

 swept away by denuding agencies, which have only left a narrow 

 fringe round the coasts as evidences of its former more extended 

 existence. Similar modifications may have taken place in many of 

 the valleys of the Highlands, although equally conclusive proofs may 

 be wanting. 



It has been frequently supposed that the directions, in which the 

 general transport in this region has taken place, indicated the opera- 

 tion of some general cause acting from north to south, or from north- 

 east to south-west. The facts, however, above stated prove, I think, 

 beyond all doubt, that the conditions, which have regulated the direc- 

 tions of dispersion from the two granitic centres described, have been 

 strictly local. 



I am not acquainted with any phsenomena within the proper 

 boundaries of the southern Highlands, which prove the depression of 

 this district during any portion of the glacial period to have been 



