D. Bell — The Great Ice Age and Submergence. 355 



been conveyed very gradually, and deposited in an extra-glaciat 

 lake, formed at this poiat along the side of the ice-sheet, into 

 which part of the materials being carried by the latter (fine mud, 

 rounded stones, shells, etc.) dropped and were accumulated. The 

 great ice-sheet which issued from Loch Ness, and turned eastward 

 along the base of the Monadhliath hills (as it was compelled to 

 do by the blocked condition of the Moray Firth and the North 

 Sea beyond) would not always, or at all. points, cling closely to 

 the base of these hills. There are bends and curves, and small 

 lateral valleys, which it would pass straight across, blocking the 

 drainage, under certain conditions, and so forming lakes of the 

 nature indicated. 



The physical configuration of the valley at this point bears out 

 the suggestion. Clava is situated right in front of such a bay or 

 recess in the hills as we have spoken of, which may very probably 

 have been barred by the ice-sheet and converted for a long time 

 into such an "area of deposition" as described. This will be seen 

 quite clearly by examining the contour lines of the locality, in any 

 Ordnance Map. 



Several of the puzzling features of the deposit may thus be more 

 or less clearly explained. The complete change which would take 

 place when the lake was formed, and while it was being gradually 

 filled up ; the accumulations of this thick mass of fine unstratified 

 silt or mud; the rounded and striated stones dropped into the heart 

 of it with scarcely any trace of sand or gravel; the shells, also, of 

 mixed kinds, but chiefly of shore species, occurring in it with a like 

 absence of the ordinary shore debris; the basin-like form of the 

 clay itself, so far as ascertained ; the overlying bed of fine sand, 

 indicating a gentle, steady current, or movement of the water, when 

 an outflow was established ; ^ and finally, the Upper Boulder-clay, 

 showing a subsequent extension, or change of direction, of the 

 ice-sheet covering up the whole;— the various parts of the section 

 seem to fall into order, and become in some degree intelligible. 

 Various confirmatory particulars might be adduced, on which, how- 

 ever, we cannot at present enter. Meantime we may say with the 

 old Latin poet — 



Si quid uovisti rectius istis, 



Candidus imperti ; si uou, his utere mecum. 



We have only to add that, while thus maintaining our ground 

 against such powerful odds, we trust we have written nothing 

 inconsistent with the respect which we have always felt towards 

 Dr. Geikie for his long and eminent services in this department of 

 Geology. 



. 1 " A velocity of 6 in. per second will lift fine sand, 8 in. will move sand as coarse 

 as linseed, 12 in. will sweep along fine gravel," etc.— Sir J. Lubbock. 



