GLACIAL BEDS. 483 



of the erratic boulders on the Jura, as the effects of ice ; but it was not until he had 

 devoted some days to the examination of actual glaciers in the Alps, that he 

 acquiesced m the correctness of Prof. Agassiz's theory relative to Switzerland. On 

 his return to Neuchatel from the glaciers of Rosenlaui and Grindelwald, he informed 

 M. Agassiz that he had noticed in Scotland and England phenomena similar to 

 those he had just examined, but which he had attributed to diluvial action ; thus 

 in 181 1 he had oljserved on the head rocks on the left side of the gorge of the Tay, 

 near Dunkeld, rounded and polished surfaces ; and in 1824, in company with 

 Lyell, he had seen grooves and striae on granite rocks near the east base of Ben 

 Nevis. About the same time Sir Cieorge Mackenzie pointed out (in a valley near 

 the base of Ben Wyvis) a high ridge of gravel, laid obliquely across, in a manner 

 inexplicable by any action of water, but in which, after his examination of the 

 effects of glaciers in Switzerland, Dr. Buckland recognized the form and condition 

 of a moraine. Eventually Agassiz and Buckland together visited some of the 

 scenes of former Glacial action in Britain, and announced the conclusions at 

 which they arrived.' That ice might have had some influence in the transport 

 of many masses of rock belonging to the "Erratic Block Group," had been 

 suggested by several observers,^ but not until clear evidence was obtained of 

 the former presence of glaciers, was the great influence of ice realized and 

 admitted. 



The more striking evidences of Ice-action to which attention 

 was first called consist of Ice-scratched boulders or stones, that 

 had been embedded in the Glacier-ice, and been scored by friction 

 against the rocky channel, or against loose fragments of rock 

 occurring in it ; Rock-surfaces and rounded eminences, smoothed, 

 polished, and striated {Roches moiitonnees of Saussure) ; Perched 

 Blocks {Blocs perches), boulders often of immense size, left at some 

 distance from their parent source in hazardous positions, such as 

 they could not have occupied if they had been ' tumblers ' falling 

 from a higher level, so that they must have been transported by 

 Glaciers or Ice-bergs, and have been left when the ice melted.^ 



The term ' Boulder Clay ' is applied to beds of a clayey or loamy 

 nature that contain angular and subangular fragments of rock, 

 and boulders, many of which are striated, and have been brought 

 from a distance. Boulder Clay may at times contain very few 

 stones or boulders, and at others be almost entirely made up of 

 them : in many parts of the Eastern Counties it is to a large extent 

 composed of Chalk. It is generally unstratified, but it contains 

 seams of sand and gravel. The term ' Till ' was first applied 

 in Scotland to the stiff unstratified clays containing angular, sub- 

 angular, and rounded blocks of rock mostly polished and striated ; 

 and it is now generally used as synonymous with Boulder Clay, the 

 accumulations being usually of a tumultuous and variable nature. 

 The term ' erratic ' is applied to boulders that have travelled long 

 distances from the parent rocks. 



Boulder Clay is directly due to the action of ice, whether in the 



1 Proc. G. S. iii. 327, 332, 345, 579 ; Buckland, Reliquije Diluviana;, pp. 

 202-206 ; Address to Geol. Soc. 1841, p. 65 ; Louis Agassiz, His Life and 

 Correspondence, by E. C. Agassiz, 2 vols. 1885, p. 263 ; Agassiz, Edin. New 

 Phil. Journ. Oct. 1842 ; see also Midland Naturalist, 1883, p. 225. 



2 De la Beche, Geol. Manual, pp. 155, 164; Lyell, Phil. Mag. (3), xvi. 348. 

 The term "Erratic Tertiaries " was used by Trimmer; and that of "Great 

 Northern Drift " has also been applied. 



^ See Hughes, Q. J. xlii, 527. 



