412 THE GEOLOGY OF 



In connection with this development of Tertiary igneous rocks in the 

 island, allusion must be made to the series of basalt and dolerite dykes so 

 largely developed in the Clyde area. They traverse all the geological 

 formations in the region and some pierce the Arran granite, facts which lend 

 support to the view that they belong to the grand outburst of volcanic 

 activity in Tertiary time in the West Highlands. 



The phenomena connected with the glacial period in the Clyde terri- 

 tory are of special interest, owing to the extent and variety of the deposits. 

 There is evidence for maintaining that, during the period of maximum 

 glaciation, this area experienced a conflict between the ice which radiated from 

 the Highlands and from the Southern Uplands. The ice that radiated from 

 the AVest Highlands moved partly down the Firth of Clyde and partly 

 eastwards towards the Firth of Forth. The striae and the dispersal of the 

 stones in the drift prove that part of the ice-stream from the Highlands 

 invaded the Clyde basin and moved south east wards to Hamilton, where it 

 was met by the ice that descended from the higher grounds in Upper 

 Clydesdale. These two opposing ice-sheets were deflected eastwards to the 

 German Ocean and westwards across the Renfrewshire Hills towards the 

 Firth of Clyde. The ice from the Highlands also overflowed the low grounds 

 of Ayrshire and coalesced with the stream that moved northwards from the 

 hills of Galloway. No less interesting is the evidence furnished by the 

 glaciation of Kintyre. That peninsula was overridden by ice which moved 

 from the Firth of Clyde in a westerly direction such deflection being due 

 probably to the influence of the ice that radiated from the north of Ireland. 



A remarkable feature of the records of glacial time in the West of Scot- 

 land is the great thickness of the superficial accumulations, which in one 

 place in the Clyde basin reaches 357 feet. The numerous natural sections 

 reveal the existence of stratified deposits in association with Boulder-clay, 

 which is confirmed by evidence from bores. The data prove the occurrence 

 of more than one Boulder-clay separated by sands, gravels, and silts. 

 Professor James Geikie and the late Mr. Dugald Bell suggested that some of 

 these interstratified deposits may have been lacustrine the lake having been 

 formed by the Loch Lomond glacier moving southwards across the Clyde at 

 Bowling towards the Kilbarchan Hills, and the waters escaping by Loch- 

 winnoch and Dairy to the Firth of Clyde. But apart from the evidence 

 supplied by the great depth of the superficial accumulations, there is clear 

 proof that the land must have stood relatively at a higher level in pre-glacial 

 time than it does now. Dr. Croll contended that the thickness of stratified 

 deposits found in the bores near New Kilpatrick in the valley of the Kelvin 

 indicated a pre-glacial channel of that river. If his suggestion be correct, 

 then the buried river-course must have entered the Clyde about 200 feet 

 below the present sea-level. This evidence is confirmed by the buried river- 

 channel that joins the Forth near Grangemouth about 260 feet below the 

 sea. Mr. Cadell of Grange has recently obtained similar evidence in the 

 case of the pre-glacial course of the river Almond, which must have entered 

 the Forth about 100 feet below sea-level. 



Underneath a thick mass of Boulder- clay in Ayrshire, both at Woodhill 

 quarry near Kilmaurs, and at Drummuir near Dreghorn, stratified beds 

 occur, that have yielded elephant tusks, antlers of reindeer, arctic ostracods, 

 and f oraminifera, together with several species of plants, including Ranunculus 

 (tquatilis and Potamogeton. Mr. John Smith has traced over a wide tract in 

 Ayrshire and as far inland as the Guelh Water near Cumnock, a thick series of 

 inter-glacial sands and gravels up to a height of 900 feet. These are 

 associated with shelly pebbly clay, which he regards as of marine origin. 

 Again, from samples of Boulder-clay near Glasgow Mr. Joseph Wright 

 obtained a large number of foraminifera which were determined by him. 

 Further on the west coast of Kintyre, at Cleongart, dark silt or clay with 



