Vol. 65.] THE CAULDRON-SUBSIDENCE OF GLEN COE. 613 



Red Sandstone plants, determined by Dr. Kidston as PsilopJiyton 

 and Pachytheca respectively, from a bed of black shale underlying: 

 the lavas on the northern face of Stob Dearg. Specimens of Psilo- 

 pJiyton were also found in dark-grey shales and mudstones under- 

 lying the basic andesites on the north side of Glen Coe above Loch 

 Achtriochtan. 1 



Mr. Kynaston published brief summaries of his researches as they 

 proceeded 2 ; but his final, and in some instances modified, conclusions 

 can only be found in the manuscript notes left by him on his de- 

 parture for South Africa in 1903. In many directions little advance 

 has been made from the position indicated in these notes. Thus- 

 Mr. Kynaston describes in detail the volcanic succession developed 

 in Aonach Dubh and Bidean nam Bian, which, as will be seen later, 

 provides a typical section of the area. He also gives an account of 

 the interesting boulders of granite, andesite, and quartz-porphyry 

 in the basement conglomerate exposed on the hillside north of Loch 

 Achtriochtan. Further, he accounted for the position of the rhyo- 

 lites of Stob Dearg, or rather the absence of the Aonach Dubh 

 andesites beneath them, by assuming an overlap of the rhyolites 

 eastwards against an uneven floor of schists. And he even inter- 

 preted the vertical junction of the volcanic rocks with the schists 

 in the Cam Glen as an extreme example of this unevenness. Here 

 again we have followed Mr. Kynaston, after a careful consideration 

 of all the evidence in the field. 



He also demonstrated that the Ben Cruachan granite is later than 

 the Old Bed volcanic rocks, since it invades and alters them ; and 

 finally we may record that in An t-Sron, above Loch Achtriochtan, 

 he had begun mapping the boundary-fault of the Glen Coe cauldron. 

 He had, in fact, realized, so far as was possible from a single section, 

 the fundamental relation subsisting between this fault and the 

 intrusive rock which so constantly accompanies it. We may illus- 

 trate this point by quoting his manuscript : — 



' On the south side of Glen Coe, south-south-west of Loch Achtriochtan, a 

 well-marked line of fault, indicated by a deep cleft on the north-east slopes of 

 An t-Sron, cuts off abruptly the basic andesites which are seen on the east side. 

 On the west side occurs a mass of granite which shows a marginal facies along 

 the line of the fault, so that it is possible that the fault may be older than the 

 granite.' 



Our own connexion with the district dates from the years 1903 

 and 1904. 3 During 1903 Dr. Peach was still in charge, and did 

 some mapping in the area himself. The time during which he was 

 actually at work in the district was very brief, but the value of his 

 influence will never be forgotten by those whom he introduced to 

 the varied geological problems of Glen Coe. 



1 'Summary of Progress of the Geological Survey for 1902' (1903) pp. 79 

 & 130. 



2 Ibid. 1900 (1901) pp. 75-85; 1901 (1902) pp. 137-40; and 1902 (1903) 

 pp. 78, 79, & 130. 



3 Cf. 'Summaries of Progress of the Geological Survey', especially those for 

 1904 '(1905) pp. 67-69, and for 1905 (1906) pp. 95-99. 



