296 E. B. Bailey— The Sgitrr of Eigg. 



EXPLANATION OF PLATE XIX. 

 All figures are magnified 50 diameters except Figs. 15c and 15d. 

 Fig. 1. Cristellaria turgidula, Eeuss. 

 ,, 2. C acutauricularis (Fichtel & Moll). 

 ,, 3. C sternalis, Berthelin. 

 ,, 4. C. cultrata (Montfort). 

 ,, 5. C. scitula, Berthelin. 

 ,, 6. C. orbiculata (Eoemer). 

 ,, la-c. C. chapma7ii, sp. nov. 7a, lateral aspect ; 7b, the same differently 



illuminated ; 7c, oral aspect. 

 ,, 8. C. erepidula (Fichtel & Moll). 



,, 9. C. gibba, d'Orh. 9(2, lateral aspect ; 9&, oral aspect. 

 ,, 10. Vaginulina inco7npta(?),'Re\iss. 



,, 11, Frondicularia gmdtirut (7), Heuss. Broken specimen. 

 ,, 12. Polymorphinafiisiformis, Eoemer. 

 ,, 13. P. problema, A^Orih. 

 ,, 14. Pulvinulina repanda (Fichtel & Moll). 14a, superior aspect; 



14&, inferior aspect. 

 ,, 15. P. caracolla (Eoemer). 15a, thin specimen; 156, thick specimen; 



15c, broken specimen showing megalospheric commencement, x 42; 



15d, broken specimen showing microspheric commencement, x 42. 

 ,, 16. P. lamplugM, sp. nov. 16a, superior aspect; 166, inferior aspect; 



16c, peripheral aspect. 



II. — The Sgure of Eigg. 



By E. B. Bailey, B.A., F.G.S. 



(PLATE XXII.) 



11HE Sguir of Eigg first attained to geological prominence in 1865, 

 when Sir Archibald Geikie in his delightful account of the 

 Scenery of Scotland offered a novel and altogether captivating theory 

 to account for its origin [I]-' According to Geikie, as all well know, 

 the precipitous ridge of pitchstone, which culminates at its eastern 

 extremity in the Sgurr, is the inverse of an ancient valley sunk by 

 a winding river in the basaltic plateau of the west. Before the 

 development of this river channel, so the theory runs, the sources 

 which had supplied the basalt lava of the plateau had already become 

 extinct ; but volcanic activity was not yet entirely banished from the 

 region, and presently a great outpouring of acid lava, entering the 

 valley, flowed for miles along its course, gradually choking it, perhaps 

 even to the brim. The resulting pitchstone has stood the test of time 

 much more securely than the neighbouring basalts, for while these 

 latter have wasted to a level in general lower than that of the old 

 valley floor, the pitchstone itself still remains in large measure 

 unaffected, and thus furnishes a somewhat battered cast of the 

 erstwhile hollow. 



The artistic appeal of Sir Archibald Geikie's conception has been 

 admitted on every hand ; but, very properly, its credentials have 

 been subjected to a dispassionate and searching scrutiny. In 1906 

 Dr. Harker, after mapping the district for the Geological Survey, 

 published an alternative interpretation of the pitchstone ridge [3j. 

 We are now asked to abandon the cherished notion of a lava moulded 

 upon the uneven contours of a river valley, and to accept instead that 

 of an intrusive sill irregular and transgressive in its own right. 

 ^ Footnote numbers in square brackets refer to Bibliography, p. 305. 



