30 A. MacEwen Pcacli — Glacial Didrihufiun of Boulders. 



of ice-flow was well to the north of east (Map 2). Ou the northera 

 shore of the Forth the farthest west point at which the boulders 

 have been found is Kosyth Church, which marks therefore the northera 

 limit of the track, the tendency of the ice-carry from Linlithgow 

 and Bo'ness, therefore, being approximately E.N.E. From Rosyth 

 to a point considerably east of jS'orth Queensfcrry a number of 

 essexite boulders are to be seen on the shore, and the northern limit 

 is again reached between Burntisland and Kinghorn, and from this 

 point eastwards along the shores of Fife to Fife Ness these essexite 

 boulders have not been observed. The northern limit of the track, 

 therefore, also lies within the boundaries of the Firth of Forth until 

 as far east as Fife Ness. At Hound Point, 35 miles from the source, 

 the last place at which an estimate can be taken, the track is only 

 some 4 miles across. From this point eastwards the southern limit 

 of the track lies within the Forth Estuary. 



The trend of these essexite erratics agrees closely with the other 

 indications of the ice-movement, such as the direction of the striae, 

 ice-mouldings, and drumlins. It may be noted that the striae (see 

 Map 1) on the high ground of the Campsie Plateau, north of the 

 boulder track, run in a direction approximately E. 30° S., making 

 an angle of about 60^ with the direction of the boulder track. This 

 apparent discrepancy is most probably due to the well-known 

 phenomenon of differential movement in the different layers of the 

 ice-sheet. The vertical distribution of the boulders is important, 

 showing that nowhere has the existence of higher ground interfered 

 with the course of the ice. During the eastward movement the 

 erratics were carried directly up from the 500 or 600 foot level to 

 over 1,300 feet in a distance of about 3 miles. 



The distribution, both vertical and horizontal, of these essexite 

 boulders points, then, definitely to the action of land-ice at a period 

 when the minor surface features of hill and dale in the central valley 

 of Scotland had little or no effect in determining the direction of 

 the ice - flow — obviously, therefore, about the period of maximum 

 glaciation. 



The distribution of the essexite exclusively to the eastward of the 

 intrusion seems to show that there cannot, at any stage of the glaciation, 

 have been a reversal of the flow in the central valley of Scotland. 

 Indeed, the narrowness of the trail formed by these boulders allows of 

 but little variation in the direction of motion. Such variation might 

 be expected if, as Professor Kendall suggests,^ the Scandinavian ice 

 ever exerted such a powerful damming effect at the mouth of the 

 Forth as to intensify the congestion in the Clyde and Irish Sea Basins. 



There is no evidence of any redistribution of these boulders by 

 later local glaciation, although local corrie glaciers are known to 

 have existed in many parts of the Campsie Fells.' Moreover, the 

 fluvio-glacial conditions which prevailed during the retreat of the 

 ice-sheet have evidently had but little effect in widening the track. 

 On the shores of the Forth, again, the action of the sea at its successive 



1 P. F. Keudall, Q.J.G.S., 1902, vol. Iviii, p. 563. 



' See E. B. Bailey, Sum. Prog. Geol. Suvv. for 190", pp. 97-8. 



