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were continuous at the time of deposition now appear in far separated 

 localities. Over the whole of this much folded and faulted series the 

 Old Red sandstones were deposited by the rivers flowing south from 

 the northern Highlands. Subsequent erosion has carried away large 

 portions of these Devonic beds, and has cut down into even the lower 

 rocks, so that the Ordovicic and Siluric are exposed in broad belts as 

 shown above, while in certain places only inliers in the Old Red have 

 as yet been exposed. To this class belong the isolated outcrops in the 



Fig. 9. Sketch Map of Southern Scotland Indicating Localittes for 

 Ordovicic and Siluric Eurypterid-Bearing Horizons 



Pentland Hills and in Lanarkshire. It is thought that in all proba- 

 bility the Wenlock and Ludlow in those regions were continuous and 

 extended southwest into Ayrshire and northeast into the Lothians. 



The Llandovery-Tarannon. In the lowest Ordovicic, volcanic 

 activities were pronounced in the Girvan area, but throughout the 

 central and northern belts of the tableland open marine conditions 

 prevailed, marked either by submarine volcanoes or by the accumu- 

 lation of radiolarian ooze, but the presence of fossiliferous mudstones 



