The Geoi.ogv oi- I.tJCHRi tiox. 27 



central line (Xo. i) again in 191 _>. Takinj; tlicsi' rt-corcls as 

 a whole, the central line becomes now the line of nearly thr 

 greatest depth. For a distance of two hundred and thirty 

 yards south of the islands ihere is an increase in depth. The 

 greatest drop at any one po'mi is 15 feet. Between \hv 

 islands, however, the sediment has risen u) feet. Considered 

 on section line Xo. i alone, there is a very large increase of 

 silt, but transverse line Xo. 15 shows a considerable narrow- 

 ing of the deepest channel, and that in spite of its removal 

 Avestw ard. 



DiTiox's Cairx. 



Dulton's Cairn may be tiic exposed porti(jn of a ledge 

 of rock reaching north to the projecting shore, or it mav 

 be the top of another moraine similar to the Merkland drum, 

 and stranded in the same way. The sudden dip on all sides 

 except that facing north would lend countenance to the latter 

 view , and also account for a prolongation of the deep chann<'l 

 between the islands in tlu- direction of the outlet. 



CoMIWRISi )XS. 



Xearly all of the smaller lochs rest wholly upon moraine 

 debris : — Lochs Mailling, I ir, Regland, Partick, Auchen- 

 crieff Loch, Collochan Loch, and Loch Aber. They are silt- 

 ing' up very rapidly. Lochs Howie, Skae, Brack, and 

 Babbington are in the last stages of existence. The largest 

 and best class of lochs lie partly upon the pre-glacial lantl 

 and partly upon moraines, ci;'., Auchenreoch, Corsock, 

 Milton, and Lochinvar. The relationship of the present 

 Lochrutton to the silted Merkland is admirably seen in 

 certain lochs in the Lake District. Buttermere and Crum- 

 mock \\'ater were prc\"iouslv one sheet, but are now 

 separated by large flats as a result of sedimentation. Oer- 

 wentwater and Thirlmere arc similarly related, but the flats 

 arc larger. The nearest approach to the Lochrutton position 

 occurs at Loch Skene in ^[offatdale. Above the loch, at the 

 foot of Broad Law, another loch existed. It has been 

 drained by the Midlaw Burn, and is now a large expanse 

 of marshy moorland. Loch .Skene is being rapidly lowered 



