62 SECTIONAL ADDRESSES. 



the sea bottom. Subsidence preparatory to mountain upheaval is a widely 

 recognised phenomenon, and further instances will be considered in the 

 course of this address. Meanwhile let us resume our journey north- 

 westwards across the Caledonian Chain. 



According to limited evidence at Lesmahagow in Lanarkshire, on the 

 Girvan-Edinburgh line, and at Stonehaven, on the Highland Border, we 

 immediately pass into a distinct mountain element characterised by 

 absence of post-Silurian unconformity. At both localities, which unfortu- 

 nately lie some forty miles apart in cross-strike measurement, the base 

 of the Lower Old Red Sandstone is seen to rest conformably on Downtonian. 

 At Lesmahagow this Downtonian is followed downwards by Ludlow and 

 Wenlock ; and then exposures cease. At Stonehaven the Downtonian, 

 2,750 feet thick, reposes with violent unconformity on greatly disturbed 

 Cambrian, or possibly Arenig. This Stonehaven unconformity may 

 reasonably be regarded as an exaggeration of the intra-Ordovician uncon- 

 formity already encountered at Girvan. 



The Cambrian, or perhaps Arenig, rocks at Stonehaven belong to the 

 well-known Highland Border series of pillow-lavas, cherts and shales. 

 They have become doubly interesting of late years since Peach and 

 Campbell and Jehu have made known their fossils. Barrow had previously 

 interpreted the Border series as steeply overthrust by the generally 

 schistose Dalradian rocks of the Southern Highlands ; and such a view 

 seems reasonable in the type section of the North Bsk. On the other 

 hand, Gunn has practically demonstrated its superposition on the 

 Dalradians in the Island of Arran. Here no sharp line of metamorphic 

 difierence has been detected ; but Gregory claims an unconformity based 

 on identification of pebbles. 



Having reached the Highland Border we are confronted with many 

 difficulties. Following Teall, I am prepared to say that we do not know 

 how far the Highland Schists are Precambrian. Most observers, like 

 Home, Barrow and Gregory, regard even their metamorphism as Pre- 

 cambrian ; but this view was always strongly combated by Peach. 

 Whatever their age, the Highland Schists admittedly lie within the 

 Caledonian mountain belt, for they are bordered on either side by intensely 

 moved Cambrian (perhaps Ordovician) fossiliferous rocks. They also 

 received additional elevation a little before and during Lower Old Red 

 Sandstone times, as is witnessed by a south-eastern fringe of tilted Lower 

 Old Red Sandstone (with Downtonian) conglomerates that remind one 

 irresistibly of the nagelfluh of the Swiss Mollasse. Moreover they were 

 the site of great volcanoes and of granitic intrusions during Lower Old 

 Red Sandstone times in a manner that co-ordinates them with the folded 

 Ordovician-Siluriau areas of the South of Scotland and the Wicklow 

 Mountains of Ireland. 



I do not propose to occupy this address with a recitation of our Highland 

 problems, but venture to touch upon three topics of particular interest. 



(1) Barrow, beginning in 1893, has drawn contours of metamorphic 

 intensity across much of the south-eastern Highlands. His has been a 

 pioneer's task and has anticipated anything of the kind attempted in 

 other countries. To-day it is finding very valuable application in the 

 south-western Highlands at the hands of Tilley and Elles. 



