TRANSACTIONS OF SECTION C. 631 



of wide distribution. The great group of dolerite sills belongs to this period. An 

 enormous number of acid and basic dykes followed, of several distinct epochs. A 

 set of minor basic intrusions of quite late date is found in the gabbro district of the 

 Cuillins, the most interesting of which takes the form of sheets of dolerite, parallel 

 at any given locality, but always dipping towards the centre of the gabbro area. 

 Mr. Harker considers that this remarkable system of injections presents a new 

 problem in the mechanics of igneous intrusion. The latest phase of vulcanicity in 

 the Cuillin district is a i-adial group of peridotite dykes. As regards the local 

 group of rock in Central Skye Mr. Harker finds that the order of increasing 

 acidity which ruled in the plutonic phase was reversed for the minor intrusions 

 which followed. 



In connection with the great development of volcanic activity in the West of 

 Scotland in Tertiary time reference must be made to the remarkable volcanic vent 

 in Arran the recognition of which is due to the suggestion of my friend 

 Mr. Peach. This volcanic centre covers an area of about eight square miles, and 

 lies to the south of the granite area of the island.^ The vent is now filled with 

 volcanic agglomerate and large masses of sedimentary material, some of -which 

 have yielded the Ehsetic and Lower Lias fossils already referred to, the whole 

 being pierced by acid and basic igneous rocks. One of the interesting features 

 connected with it is the occurrence of fragments of limestone with the agglomerate, 

 which has yielded fossils of the age of the chalk, thus proving that the vent is 

 post-Cretaceous. There is thus strong evidence for referring the granite mass in 

 the north of the island and most of the intrusive, acid, and basic igneous rocks to 

 the Tertiary period. It furnishes remarkable proof of the suggestion of the 

 Tertiary age of the Arran granite made by Sir A. Geikie in 187.3.'* The story 

 unfolded by this discovery is like a geological romance. The former extension of 

 Rha3tic and Lower Lias strata and of the chalk in the basin of the Clyde, and the 

 •evidence of extensive denudation ni the south of Scotland, appeal vividly to the 

 imagination. 



This outline of the researches in the solid geology of Scotland would be 

 incomplete without reference to the publication of Sir A. Geikie's great work on 

 ' The Ancient Volcanoes of Great Britain ' (1897), in which the history is given of 

 volcanic action in Scotland from the earliest geological periods down to Tertiary 

 time. To investigators it has proved invaluable for reference. Nor .can I omit to 

 mention the new edition of his volume on ' The Scenery of Scotland,' wherein he 

 depicts the evolution of the topography of the country with increasing force and 

 fascination. In this domain it may be said of the author, ' Nihil tetigit, quod non 

 ornavit.' 



From the brief and imperfect sketch which I have tried to give of recent 

 advances in the solid geology of Scotland it will be admitted that restless activity 

 and progress have been characteristic of the last quarter of a century. But we 

 may expect that the conclusions accepted now will be rigorously tested by our 

 successors, probably in the light of new discoveries and with more perfect methods 

 of research. It is well that it should be so, for thereby our branch of science 

 advances. Meanwhile, as we look back on the phalanx of geologists that Scotland 

 has produced— to Hutton and Hall, Murchison and Lyell, Hugh Miller and Fleming, 

 Nicol and Ramsay — and reflect on the services which they rendered to geology, we 

 may hope that this record of progress may prove a fitting sequel to the labours of 

 these illustrious men. 



The following Papers and Report were read : — 



1. Recent Discoveries in Arran Geology. 

 By William Gunn, of H.M. Geological Survey of Scotland. 



In the last ten years very important additions have been made to our know- 

 ledge of the geology of Arran both in the aqueous and in the igneous rocks of the 

 island. 



' Quart. Jmirn. Geol. Soc, vol. Ivii, p. 226 (1901). 

 " Traihs. Geol. Soc. Edin., vol. ii. p. 305. 



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