Notices of Memoirs — Prof. J. Preshcich. 321 



have swept across the Atlantic to our shores, and was made answer- 

 able for every unaccountable phenomenon in surface geology pre- 

 sented to their notice. A more probable theory is, that they were 

 carried over by icebergs, but this necessitates that the land be 

 submerged to the depth of 700 or 750 feet, and if that be granted, 

 there can be no reason why the ice-floes should not have been 

 occasionally stranded on some of the higher lands below the level of 

 the water, and there have left evidence of their presence in heaps of 

 travelled boulders, as well as in the lower parts of the valley ; but 

 such evidence is enth-ely wanting. 



On the other hand, the glacial clays are extended across the mouth 

 of the Calder, and the boulders derived from them may have been 

 washed into the valley, during a slight submergence, by the action of 

 the tides and waves and also borne up the valley by ice-floes. The 

 statement of Prof. Green that a glacier at one time extended as far 

 south as Barnsley, and left its detritus spread over the country 

 northwards, furnishes a source for the boulders actually within the 

 valley of the Calder as far west as Wakefield, and during the denu- 

 dation of this district by marine action, the boulders would be 

 naturally washed into the sheltered bay which the valley under 

 those circumstances would form. It is not necessary that the land 

 should be submerged more than 250 or 300 feet ; but if it was 

 lowered to the extent of about 350 feet, there is evidence of its 

 former presence in the beds of sand and gravel which are found in 

 many places on the hill-sides at a nearly uniform height above the 

 sea-level. 



1TOTICES OIF ZMHEIMIOIIRS. 



Eoyal Society of London, May 1st, 1879. 

 On the Origin of the Parallel Eoads of Lochaber, and 

 their Bearing on other Phenomena of the Glacial Period. 

 By Joseph Prestwich, M.A., F.K.S., F.G.S., etc., Professor of 

 Geology in the University of Oxford. 



A PAPER bearing the above title was read before the Eoyal Society 

 on May 1st, in which the author gave a fresh interpretation 

 to these well-known terraces. He commenced by stating that 

 of the various hypotheses that have been brought forward since 

 the time of Macculloch and Dick-Lauder to account for the origin 

 of the Parallel Roads of Glen Eoy, the one so ably propounded 

 by Mr. Jamieson, in 1863, has been most generally received and 

 adopted. It is a modification of the views originally expressed by 

 Agassiz, to the effect that the barriers of the lakes — to the shore 

 action of which both the above-named geologists attributed the 

 " roads." but were at a loss to account both for the formation and 

 removal of barriers — had been formed during the Glacial period by 

 glaciers issuing from Glen Treig and Glen Arkaig, supplemented by 

 others from Ben Nevis. The subsequent determination, by the 

 Scotch geologists, of an intermediate milder period succeeded by a 

 second cold period, led Mr. Jamieson, with whom the preglacial and 



DECADE II. VOL. VI. — NO. VII. 21 



