ON THE SHELL-BEAEING DEPOSITS AT CLAVA, AND OTHEU PLACES. 513 



It is difficult also to see how the ' upper boulder clay,' said to have 

 been formed by the ' second,' or post-submergence, glaciation could fail 

 to be thickly charged, in almost every locality, with remains of marine 

 organisms dez-ived from the miles upon miles of former sea-bed over 

 which the ice must have passed. 



From what we know of the configuration of the district and of its 

 glaciation we are convinced that, owing to the immense pressure of ice 

 from the mountains to the west, and the blocked condition of the Moray 

 Firth and the North Sea during-the Glacial period, ice on a great scale, 

 issuing from Loch Ness, was deflected eastwards along the base of the 

 Monadhliath mountains; that this deflection began at a considerable 

 distance south of the present mouth of the loch; and that such ice 

 passed over Clava. This conclusion is supported by the strise and the 

 distribution of boulders throughout the Nairn valley, and on towards 

 Forres a,nd Elgin. The stri^ on some higher parts of the Monadhliath 

 hills pointing north, north-west, &c., we view as belonging to an earlier 

 stage of the glaciation, before the congestion in the Moray Firth took 

 place. • Unless the different stages and changes of direction of the 

 ice-sheets as they reached their maximum be kept in mind, we submit 

 that a ' map of striae ' of almost any district is unintelligible. 



The ice-transport theory, therefore (whatever difficulties may attach 

 to it), has at least this point in its favour, that the deposit is quite in 

 the track of ice which would almost certainly pass over part of a former 

 sea-bed in its progress. ^ It has also this other point, that the shelly 

 clay consists almost wholly of materials derived from some distance, 

 differing from those in the immediate neighbourhood, and from the 

 boulder clay and gravel both above and below it. Further, though the 

 clay itself suggests deposition in deep and comparatively still water, the 

 shells and other organisms it contains are almost entirely of littoral 

 species ; and though the stones in it are in general rounded and water- 

 worn, some distinctly striated are associated with them, and all occur 

 promiscuously imbedded in this fine unstratified clay without, as a rule, 

 even a streak of accompanying sand or gravel. 



Mere 'submergence' seems inadequate to account for these facts. 

 And we venture to say that to assume, first, a submergence of over 

 500 feet, then a re-elevation to about the old level, with a return of 

 glacial conditions, much the same as before, is to hang an immense 

 series of changes upon the (as regards interpretation) more or less 

 doubtful evidence before us. 



Our observations have convinced us, generally, that no such sub- 

 mergence, nor any at all approaching to it, took place in any part of 

 the British Isles during the Glacial epoch. 



On the other hand, we freely admit that the extent of the shelly clay 

 in this instance and the perfectness of many of the contained shells do 

 weigh against the supposition that the deposit, as a whole, owes its 

 transport, or at least its present form, to land-ice. The objection from 

 the comparatively perfect condition of the shells is perhaps the most 

 important. Whether, in view of the known instances in which even 



' These strise may partly belong also to a later time after the congestion had 

 given way, but for various reasons we are disposed to assign them mainly to the 

 earlier stage. 



- A submergence of only 60 feet would make Loch Ness an arm of the sea, with 

 a long, comparatively shallow bay at its seaward end. 



1893. L L 



