THE GEOLOGY OF THE CLYDE TERRITORY. 



BY J. HORNE, F.R.S. 



THIS district embraces the natural drainage area of the River Clyde and of 

 the sea-lochs that form extensions of its estuary. Northwards the boundary 

 line is defined by the mountains round the head of Loch Fyne and Loch 

 Lomond ; eastwards by the watershed between the Clyde and the rivers 

 flowing east to the German Ocean; and southwards by a line drawn from the 

 Mull of Kintyre to the southern point of Ayrshire. It thus comprises a 

 broad belt of crystalline schists extending from Loch Lomond to the Mull 

 of Kintyre, a portion of the Silurian tableland of the Southern Uplands and 

 a great development of Old Red Sandstone and Carboniferous strata occupy- 

 ing the western part of the Central Lowlands. 



The southern limit of the crystalline schists of the southwest Highlands is 

 defined, between Loch Lomond and Toward Point south of Dunoon, by 

 powerful faults which let down the Old Red Sandstone on the southeast side. 

 Immediately to the north of this fault, between Loch Lomond and Callander, 

 there is a narrow belt of strata, provisionally correlated with the Arenig 

 rocks of the south of Scotland, including hornblende-schists, chlorite-schists, 

 cherts, black shales and grits. Similar strata have been recently identified by 

 Mr. Gunn of the Geological Survey in North Glen Sannox, Arran, and they 

 have been traced at intervals along the Highland border by Messrs. Barrow, 

 Dakyns, and Clough, to Forfarshire and Kincardineshire. In Arran the 

 green rocks of igneous origin comprise lavas, volcanic agglomerates and 

 intrusive masses which recall petrological types of the Arenig igneous rocks 

 in Ayrshire. Both in Arran and in the Kelty Water near Callander these 

 strata are considerably deformed ; the igneous rocks have been rendered 

 schistose, the black shales are cleaved, the cherts have been granulitised, and 

 the grits show flaser structure. Though the black shales have yielded 

 impressions which simulate the appearance of graptolites, it must be frankly 

 stated that no fossils have been obtained from these rocks which prove their 

 age. In Forfarshire, Radiolaria have been found in the cherts, and certain 

 rounded bodies have been detected in the same rocks in the Callander region 

 which may prove to be traces of these organisms. The relation of these 

 presumably Silurian rocks to the schistose grits of the Highlands, both near 

 Loch Lomond and in Arran, is still uncertain. In Forfarshire and Kincardine- 

 shire Mr. Barrow of the Geological Survey has drawn a reversed fault 

 between the two, but no such line of displacement has yet been detected in 

 the southwest Highlands. Indeed the boundary line must be regarded as a 

 provisional one in the Callander district and in Arran. 



To the north of the belt of strata just described there is an important 

 development of altered sedimentary rocks forming the crystalline schists of 

 the Eastern Highlands. The various subdivisions are arranged in a definite 

 order, but it is uncertain whether it indicates the original sequence of 



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