OE THE OUTER HEBRIDES. 867 



Note. 



In the discussion that followed the reading of this paper, Pro- 

 fessor Judd is reported to have said that erratics derived from the 

 western islands occur upon the mainland. I suppose Mr. Judd 

 refers to some large blocks of a dark gabbro which are found in the 

 vicinity of Loch Creran, and which are similar in character to the 

 gabbro of Mull. But Mull is not the only place in Scotland where 

 gabbro occurs ; and for many reasons, which need not be pointed out 

 here, it is in the highest degree unlikely that the Loch-Creran 

 erratics came from that island. Their parent rock will probably be 

 found in Dalness Forest or the heights above Glencoe. I have 

 never seen upon the mainland any erratics which could be shown to 

 have come from the Inner or Outer Hebrides ; but it is quite pos- 

 sible that such may yet be detected at low levels — in such districts, 

 namely, as were submerged in late glacial times. 



September, 1878. 



EXPLANATION OF PLATE XXXIII. 



Map of the Outer Hebrides and the Minch, showing the direction of glacia- 

 tion and the position of submerged rock-basins. The soundings are from the 

 Admiralty charts ; but these are given only in sufficient numbers to indicate 

 the general configuration of the sea-bottom. 



Discussion*. . 



The President called attention to a point not noticed by the 

 authors who had dealt with changes of climate, namely, that we are 

 not justified in assuming that the amount of heat given out by the 

 sun in past times has been always the same. It was quite possible 

 that it might have varied ; and this should be borne in mind in all 

 speculations on the subject. 



Mr. J. F. Campbell confined his remarks chiefly to the first 

 paper, as he did not believe in general glacial periods. As there 

 are terraces on the banks of the Mle, marking water-levels half a 

 year old, so in Britain and Western Europe terraces and shells prove 

 that the sea has stood 1200 feet higher : at different levels tides 

 would carry floating ice to and fro in channels, so as to score rocks. 

 The arrows in Mr. Geikie's Map of the Hebrides point in all direc- 

 tions. Whence ice came to score certain rocks to which Mr. Camp- 

 bell referred in a former paper, was another question. He had sug- 

 gested from the N.W. ; Mr. Geikie has said from S.E. The rocks of 



* This discussion related to two other papers read the same evening, but 

 which have since been withdrawn. These were entitled, " Cataclysmic Theories 

 of Geological Climate," by Dr. James Croll (now published in the ' Geological 

 Magazine' for Sept. 1878), and " On the Distribution of Ice during the Glacial 

 Period," by T. F. Jamieson, Esq., F.G.S. 



3m2 



