Vol. 52.] THE TERTIARY BASALT-PLATEAUX OP N.W. EUROPE. 331 



19. The Tertiary Basalt-plateaux of North-western Europe. By 

 Sir Archibald Geikie, D.Sc, LL.D., F.R.S. (Kead December 

 18th, 1895.) 



[Plates XV.-XIX.] 



Contents. 



Page 



Introduction 331 



I. The Plateau-Lavas 332 



II. The Vents 342 



III. The Eivers of the Volcanic Period 354 



IV. The Basic Sills 373 



V. The Dykes 382 



VI. The Intrusive Gabbros 384 



VII. The Granophyre Intrusions 389 



VIII. Modern Volcanic Action in Iceland, as illustrative of the 



History of the Basalt-plateaux of North-western Europe . 395 



IX. The Faults of the Plateaux 399 



X. The Effects of Denudation 402 



Introduction. 



'Since the publication, seven years ago, of my memoir on ' The 

 History of Volcanic Action during the Tertiary Period in the 

 British Isles,' 1 I have continued the investigation of this subject. 

 My researches in this interval have included a re-examination of 

 various tracts in Mull, Rum, Raasay, and Skye ; numerous traverses 

 in the last-named island, especially over areas which had not been 

 previously described by any geologist : a detailed survey of Canna 

 and its adjacent islets ; an exploration of the Shiant Isles and other 

 insular outliers of the Tertiary sills, and a visit to St. Kilda for the 

 purpose of accurately determining the relations of its two great 

 groups of igneous rocks. In two successive years I have prolonged 

 my excursions into the Faroe Islands, where the phenomena of our 

 basaltic plateaux are reproduced on a colossal scale, and where the 

 numerous fjords and sounds have laid bare the most stupendous 

 range of geological sections. This extended series of observations, 

 while entirely confirming the main conclusions announced in my 

 former memoir, has furnished many fresh and important illustrations 

 of phenomena already described, and some new and interesting 

 additions to our knowledge of the volcanic history of Tertiary time 

 over the North-west of Europe. I now lay before the Society an 

 outline of the chief results which have thus been obtained. 2 



1 Trans. Roy. Soc. Edin. vol. xxxv. (1888) pp. 21-184. 



2 It is a pleasure to acknowledge the great assistance which has been kindly 

 afforded to me in these researches. I am specially indebted to my friend 

 Mr. Henry Evans, who, by placing his steam-yacht Aster at my disposal, 

 enabled me to visit many localities among the Inner Hebrides and outer islands 

 which are not easily accessible, and to make acquaintance with the whole group 

 ■of the Faroe Islands. His brother, Col. John Evans, photographed for me 



