290 PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [May 12, 



flomng through the old channels, would tend to cut them down to 

 these levels ; whilst the sudden rise of the land would stop the 

 further continuation of the process. It is also important to remark 

 that at all these points a stream enters the main valley from the 

 side, or from a lateral valley, and thus, by the debris it would bring 

 down and deposit at its mouth, would tend to fill up the main valley 

 to the level of the line. This is very markedly the case with the 

 pass of Maecoul and that of Glen Glaister. It may also be noted 

 that such coincidences of the lines with hollows between the hills 

 are seen in other places. Such is that already mentioned of the 

 coincidence of the upper line with the level of Loch Ericht and the 

 watershed between the basins of the Spey and the Tay. 



But it must be remembered also that difficulties do not affect only 

 this theory. Perhaps the combination of the various conditions 

 needed to shut and open the lake-barriers exactly at the right time 

 and in the proper order are not more probable. If these lake-bar- 

 riers were formed of detritus, its collection and sudden removal is 

 no less inexplicable. Ice-barriers may seem more manageable, but 

 are subject to no less inexorable conditions of climate and elevation. 

 A glacier that would fill the valley of the Spean and Roy with a 

 mass of ice 800 or 1000 feet thick, and some miles in extent, would 

 require an extent of feeding- ground that is not easily found in this 

 region. I have never heard of a lake of such depth shut in by ice 

 in any part of the earth at the present time. To form an embank- 

 ment for a water reservoir of one-fourth the depth and one-tenth 

 the extent of the supposed Glen-Eoy lakes, with the best materials 

 he can select, is no mean task for an engineer of the present day. 

 What would he think of the task were he required to build the 

 barrier of a material of less specific gravity than the water to be 

 shut in, of a material which that water and the ground on which it 

 rests were constantly corroding and wasting away, so that his bar- 

 rier had to be incessantly moving forward from behind to compensate 

 for what it lost in front ? To form a permanent lake with a uniform 

 level on such conditions has, I must confess, always appeared to me 

 an almost impossible problem, far outweighing any difficulties that 

 attach to the marine theory. 



But all such considerations may be laid aside. The chief and 

 fatal objection to the lake-theory is that it supposes rivers to have 

 fiowed in places where there is clear proof that no river has ever 

 flowed,— that it assumes a great lake to have been suddenly drained 

 by a narrow glen where it is undoubted no stream of water, larger 

 or more rapid than the tiny rill gathered from the sides of the 

 neighbouring mountain, has ever existed since the ocean laid down 

 the loose soil spread over its smooth unbroken declivities. The 

 theory not only fails to explain the phenomena, but is in direct con- 

 tradiction to them, and therefore must be rejected. 



Discussioif. 

 Mr. GwYF Jefpeets observed that no organic remains appear to 

 have been found in these beaches, £o as to prove their marine origin. 



