1 1 2 Glacial Conglomerates. 



intervals to the Forth, near Bridge of Allan. The 

 ordinary sedimentary conglomerates are frequently very 

 coarse, containing both water-worn and subangular 

 fragments of the underlying rocks from the waste 

 (denudation) of which it has been formed. Some of 

 the fragments I have observed of a yard in diameter, in 

 the great band of conglomerate that lies at the foot of 

 the Grampian Mountains, and others, true boulders, of 

 equal size, on the north coast of Scotland, east of 

 Strathie in Caithness. The Silurian gneiss of the 

 Grampian Hills and of the Highlands in general, is 

 much older than the Old Red Sandstone, and the same 

 may be said of the strata of the Lammermuirs, both of 

 which were disturbed and denuded before the depo- 

 sition of the Upper Silurian rocks. Later denudations 

 of the same rocks formed the vast conglomerate of Old 

 Red rocks south of Dunbar. 



Some of these conglomerates possess a character 

 which unmistakably marks them as glacial boulder 

 clays. The stones are of all sizes, and not mere pebbles, 

 and they are generally sub-angular, just like those of 

 many of the boulder clays of the last Glacial Epoch. Like 

 some of these boulder clays also, the stones are imbedded 

 in a red marly paste, once un consolidated clay, and in 

 similar conglomerates in the Cumbrian region, scratched 

 stones have been found in some cases unmistakably 

 resembling those which are allowed by all to have had 

 their markings produced by the agency of glacier ice. 

 A bold man might even go further, for opposite the 

 mouth of the valley of Ullswater, at the outlet of the 

 lake, there are great heaps of angular boulder-con- 

 glomerate, culminating in the big mound-like hills of 

 Mell Fell and the neighbourhood, the stones cemented 

 in a marly base. It is an obvious fact to skilled 



