524 THE DRIFT OR GLACIAL FORMATION OF 



Clyde in Ayrshire I have seen no Arran granite above the 100 feet contour, 

 and very little below it, indeed not more that might have been introduced 

 by human agency. In the island itself many large granite blocks have come 

 east. A few north Highland schistose rocks are abundant in the northern 

 part of the Clyde area, and extend as far S. as Muirkirk (perhaps to Wanlock 

 Water). They have been long known to the country folk as " Heelan Whin." 

 Boulders of mackled granite, possibly from Ben Cruachan, but more probably 

 from the patch of similar granite which lies E. of the head of Loch Fyne at 

 Loch Garabal, 1 diorite from Glen Falloch, and actinolite (hornblende) probably 

 from near Loch Tay, are occasionally got. Knype granite from New Cumnock 

 is found towards the head-waters of the Clyde, more especially in the district 

 between the Lowthers and the Crawick Water. 



Spango granite is frequent about Muirkirk, Douglas Water, and the head- 

 waters of Glenmore Water and Crawick Water. On a recent investigation I 

 found that the Spango granite boulders extended for several miles all round 

 the outside of the granitic area. Watstone Hill granite is frequent in the 

 upper part of the Irvine valley, but less so about Strathavon, an occasional 

 block having found its way as far to the N.N.W. as Kilwinning and as 

 far E. as the Nethan Water. The granite to the south of Loch Doon and 

 Loch Bradan is found in immense quantities in the valleys of the Doon and 

 the Girvan, and along the Carrick shore, and has come N. as far as Portin- 

 cross, and S. to Lead hills as seen in recent railway cuttings, and also some 

 way West. Boulders are sometimes seen lying with their long axes in the 

 same direction as the rock-striae, but they are also found lying across them, 

 in fact in all ways, and sometimes even standing perpendicularly in the drift. 



ROCK-STRIAE. 



Perhaps these should have been partly treated of first of all, but it is 

 extremely difficult to discriminate between the first formed striae and the 

 later ones. Those on rock-faces are often taken as indexes to the direction 

 from which the drift was carried along and deposited by land-ice, but I 

 believe the striae have nothing to do with the drift-beds above them. It is 

 evident that glacier-ice was in motion long ages before they were deposited, 

 the old rotted rocks having in many parts been previously removed ; and the 

 condition of the majority of the stones and boulders in the drift shows that they 

 were derived from solid rock and not from the rotted surface-rock. At the 

 present day, for instance, solid serpentine cannot be got from the outcrops, 

 except on the sea-shore or from underdrift, but it can be obtained in first- 

 rate condition from the Boulder-clays of Lendalfoot, etc. Where the bottom 

 beds of drift are composed of gravel there are no striae on the rock-faces 

 under it. In the higher reaches of the Clyde area some of the rotted grey- 

 wacke and Spango granite may date from pre-glacial times. 



The directions of the rock-striae in the Clyde area are briefly : On the 

 Ayrshire coast, S. of, or parallel to, the coast-line ; in the lower part of the 

 Doon valley, N.W., or with the valley ; at Loch Doon, nearly N., or with the 

 valley and loch ; in N.E. Ayrshire, S.W., or with the valleys ; in the upper 

 hilly part of the Garnock valley, S.E., or with the valley ; on the head 

 waters of the Irvine, W., or with the valley ; at Fairlie, S., or with the shore 

 (or Clyde valley) ; at Little Cumbrae, the same ; in Renfrewshire, from 

 Greenock to Paisley, E.S.E. ; on Loch Lomond, S.S.E., or in the direction of 

 the loch ; at Airdrie, E. ; at Lanark and Carnwath, E.N.E. ; in Bute, S.S.E., 

 the direction of the Firth of Clyde valley ; on the upper part of Loch Fyne, 

 S.S.W., or with the loch ; in the lower part of Kintyre, both across and with 

 the long axis of the peninsula. 



It will be seen from this that the direction of the striae generally follows 

 the slope of the ground (though sometimes they are at right angles within 



1 Hopkins, Q. J. G. S., 1850. 



