E. B. Bailey — The Sgurr of Eigg. 297 



The rumour that the familiar theory had been set aside by so 

 competent an authority created a feeling akin to consternation. 

 Accordingly in 1905, before the publication of the paper just referred 

 to, Dr. Peach joined Dr. Harker iu a re-examination of the crucial 

 sections. 



Dr. Peach started with a predisposition in favour of Geikie's 

 position, but returned fully convinced by Harker's demonstration of 

 the alternative hypothesis. However, quite undeterred by this 

 notable conversion, 8ir Archibald Geikie maintained a position of un- 

 compromising hostility when Harker delivered his paper before the 

 Geological Society of London [3, Discussion, p. 67]. 



Under these circumstances several of us have experienced a not 

 unnatural desire for personal contact with the evidence. In my own 

 case this desire has now been gratified, for I spent a large part of 

 three days last September reviewing the phenomena upon which 

 Geikie and Harker have concentrated our attention. 



There is no excuse at the present stage for a further detailed 

 account of the Sgiirr. What I propose is merely a discussion of 

 Dr. Harker's paper. I am certain that readers will share my 

 gratitude to Dr. Harker himself for allowing me, with the sanction of 

 the Council of the Geological Society, to reproduce Figs. 1, 2, and 3, 

 which have already appeared in the pages of the Quarterly Journal. 

 To Mr. A. Stenhouse we are equally indebted for a hitherto un- 

 published photograph (PI. XXII, Fig. 1), which I consider an ocular 

 demonstration of one of Harker's main criticisms of Geikie's description. 

 To Mr. Rhodes, jun., we owe the microphotograph (PI. XXII, 

 Fig. 2) taken from a specimen collected by myself and now deposited 

 with the Geological Survey ; this microphotograph will probably 

 induce many to join with the present writer in accepting Geikie's 

 interpretation as essentially correct, in spite of the error alluded to 

 above. 



Internal Intrusion Phenomena. 



Sir Archibald Geikie in his early descriptions, and also in his reply 

 to Dr. Harker's criticisms, has laid great stress upon the quite 

 definite stratification of parts of the pitchstone ridge. The inter- 

 pretation he offers is that the acid lava filled up the old valley in 

 recurrent superimposed sheets of pitchstone and porphyry. In this 

 particular Dr. Harker has furnished an important correction which 

 I am prepared to endorse without reservation. He points out that 

 the supposed porphyry lavas (Harker uses the term felsite) are in 

 reality intrusions cutting the pitchstone mass after the latter, in 

 consolidating, had assumed its columnar jointing (Text-fig. 2). 

 A particularly convincing example of this relation is illustrated 

 iu Mr. Stenhouse's photograph (Pi. XXII, Fig. 1). The porphyry 

 or felsite of these intrusive sills is of essentially the same material 

 as the pitchstone itself; the difference is that the former has a more 

 stony, the latter a more glassy, base. Dr. Harker emphasizes the 

 close connexion of the two rock-types by an important observation 

 which, in the limited time at my disposal, I left unchecked. He 

 finds that certain of the definitely intrusive felsite sheets, when 

 followed along their outcrop, merge by insensible gradations into the 



