48 Correspondence — Tlie Sgurr of Eigg. 



by Koenig in 1818, and therefore is not preceded by Proteosaurus 

 Home, 1819. 



J. Allan Thomson. 

 Dominion Museum, Wellington, N.Z. 

 October 3, 1919. 



THE SGUKR OF EIGG. 



Sir, — My attention has been called to this time-honoured contro- 

 versy by the contributions to the subject by my friends Dr. Harker 

 and Mr. E. B. Bailey. 



In 1898 I mapped the Sgurr very carefully on the scale of 

 6 inches to the mile, and obtained a good deal of evidence that 

 has not yet been published. 



For instance, there are pebbles of granite in the Bidein Boidheach 

 conglomerate, granite of a Tertiary type and resembhng none of 

 the older granites in Scotland. This certainly suggests that the 

 conglomerate or breccia is of late date and not of pre-dolerite age. 



The dolerite sill (if it be a sill at all) at Bidein Boidheach does not 

 turn upwards at the junction, but is cut off abruptly. The basalt 

 dyke at the same place is also cut off, in my opinion. I have never 

 seen any fragmental deposit that could stop a basalt dyke that 

 had pierced through a succession of lavas. 



I made many observations of the inclination of the base of the 

 pitchstone, and there is no doubt that rock occupies a very distinct 

 and deeply cut groove in the basalt lavas and dolerite sills. 

 Incidentally I may mention that in my opinion the sills are far 

 fewer than Dr. Harker Avould suggest. 



The bottom breccia at the base of the Sgurr (eastern end) I took 

 to be, as Dr. Harker says, part of the pitchstone, but not intrusive. 

 As I read the evidence, it is the brecciated base of the flow over 

 which the rest flowed. It has picked up fragments of basalt, sand- 

 stone, wood, etc., and rolled along under the main mass. A coating 

 of glass round basalt fragments is quite to be expected. I have never 

 seen any intrusion that acted in quite the same way, though I have 

 seen igneous breccias formed at the edges of intrusions. 



I left Eigg quite convinced of the general accuracy of Sir Archibald 

 Geikie's theory, and nothing that I have read since has induced me 

 to change my opinion. 



Dr. Harker's theory rests on too many theoretical considera- 

 tions ; Sir Archibald Geikie's theory, especially as championed by 

 Mr. Bailey, rests chiefly on field evidence. In such cases, from a 

 long and very varied experience of field-work all over the world, 

 I naturally give the greatest weight to field evidence, and though 

 I do not wish to belittle any of the microscopic evidence that 

 Dr. Harker has brought forward nor to disregard any of the 

 -arguments he has advanced, I cannot accept his theory. 



E. H. Cunningham-Craig. 



