Dugald Bell — Glacial Mound in Glen Fruin. 415 



ginous grit-stone ; probably from the Karoo Beds. 15. Sandstone ; 

 from the Karoo Beds. Nos. 13 to 15 have been drifted from the 

 Stormberg and neighbourhood higher up the country. 16. Pebble 

 of brown quartzite ; possibly from the Karoo Beds. 



17. Mundic in slate. 18. Siliceous schist, or brown banded 

 lydite. 19. Jasper. 20. Vein-quartz. Nos. 17 — 20 have been 

 derived from the old rocks ; probably having been brought up from 

 below, but possibly drifted on the surface. 



The mineral contents of the diamond-matrix or " Blue Ground " 

 of Kimberley (De Beer's, etc.) were described by the late Professor 

 H. Carvill Lewis in the Geol. Mag. 1887, pp. 22-24. 



The diamond-yielding gravel of the Vaal Eiver, partly drifted 

 from the igneous and the old rocks of the higher country on the 

 East, and partly derived from diamantiferous necks and patches, has 

 much analogy to that of the refuse-heaps or washed stuff of the 

 diamond-mines. The constituents of the Vaal gravel, and of that 

 of Dutoit's Pan, are enumerated in the Geol. Mag. 1871, pp. 55, 

 56 ; and Quart. Journ. Geol. Soc. vol. xxviii. 1871, pp. 17-21. 



VII.— On a Glacial Mound in Glen Fruin, Dumbartonshire. 



By Dugald Bell, 



Geological Society of Glasgow. 



GLEN FRUIN ' is a quiet secluded glen, about six miles in length, 

 extending in a north-westerly direction between Lochlomond 

 and the Gareloch, and opening off the neck of land which divides 

 those lochs at between 200 and 300 feet above the sea. To the 

 south-east, it slopes towards Lochlomond, of which the Fruin water 

 is one of the principal affluents. On the west it is divided from the 

 Gareloch by a range of hills 1000 or 1200 feet in height, which at 

 its upper extremity subside into a col or pass of 600 or 700 feet. 

 This upper part of the glen is composed of the mica and clay slates 

 common to the Western Highlands. The lower part is formed of 

 beds of the Calciferous Sandstone series, which have here been 

 faulted down against the older formations. 



The upper part of the glen bears every indication of having been 

 at one time occupied by a lake. 



A huge boulder of mica-schist, resting on the sandstone, occurs 

 near the foot of the glen, and there are many smaller ones in the 

 same neighbourhood. The respected Convener of the Edinburgh 

 Boulder Committee, the late Dr. Milne-Home, thought this large 

 boulder had been brought by an iceberg (which was his favourite 

 means of transport) either coming down Lochlomond and drifting 

 aside into Glen Fruin, or more probably finding its way over the 

 head of the glen during a period of " great submergence." 



The iceberg hypothesis seems to be attended with insuperable 

 difficulties, when we consider (1) where such large icebergs could 

 be formed in the event of so great a submergence as the theory 



1 The " Glen of Sorrow," scene of a sanguinary conflict between the Colquhouns 

 and Macgregors in 1603. (See Introduction to " Eob Eoy."j 



