E. B. Bailey — Iceland, a Stepping -Stone. 467 



Geikie drew the greater part of his informatiom from Thoroddsen's 

 writings, supplemented by those of Helland, Tempest Anderson, 

 and Johnston-Lavis. His theme throughout was the conspicuous 

 and abundant evidence afforded of fissure eruptions. 



Since then various other publications have appeared dealing in 

 English with the volcanic phenomena of Iceland. Of these we may 

 mention thi'ee in particular: — 



In 1901 Thoroddsen brought out his Geological Map of Iceland on 

 the scale of 1 : 600,000. It is a truly magnificent achievement, 

 representing much of its author's life-work in the field from 1881 

 onwards to 1898. 



In 1909 Suess supplied further summaries of Thoroddsen's 

 results, especially in regard to ring-fractures, cauldron-subsidences, 

 and earthquakes. His descriptions, accompanied by two of 

 Thoroddsen's small-scale maps, will be found on turning to vol. iv, 

 p. 262, of the Sollas (English) edition of The Face of the Earth. 



In the same year Clough, Maufe, and the present writer con- 

 tributed a resume of Spethmann's 1908 paper 1 on Askja, Iceland's 

 greatest volcano. This short account is illustrated by Spethmann's 

 own map, and starts on p. 666, vol. lxv (1909) of the Quarterly 

 Journal of the Geological Society. Its intention is to facilitate 

 comparison between the cauldron-subsidences of Askja, in Iceland, 

 and of Glen Coe, in Scotland — Askja, of post-Glacial age, with its 

 deep caldera and its rim-craters and solfataras; Glen Coe, of Lower 

 Old Red Sandstone age, with its caldera form obliterated by erosion 

 and its external ring of intrusions bared b} r the same agency. 



Since Glen Coe was described much has been written by members 

 of the Scottish Geological Survey on ring-fractures and ring- 

 intrusions; notably by Maufe in relation to Beri Nevis, and by 

 Wright, Richey, Clough, and myself in regard to Mull. As time 

 goes by the value of a knowledge of Thoroddsen's observations in 

 Iceland becomes more than ever apparent. Accordingly some years 

 ago I prepared an abstract of " Die Bruchlinien Islands und ihre 

 Beziehungen zu den Yulkanen ", 2 a paper already referred to by 

 Suess. This abstract, rearranged, forms Part 2 of the present 

 communication. Part 3 is a definitely speculative venture, in 

 which Suess is in large measure adopted as guide, though in certain 

 important matters his conclusions are set aside. 



The raap of Iceland, p. 468, is based essentially on Thoroddsen's 

 1905 map, somewhat reduced in scale, and with the earthquake 

 districts and much of the topography omitted. The outcrop of the 

 Older Tertiary Lavas is an additional feature derived from 

 Thoroddsen's 1901 map. It should also be pointed out that 

 Thoroddsen merely shows the Askja Caldera as a geographical 

 feature, whereas in accordance with Spethmann's observations 

 I have ventured to surround it by a ring-fault, with a minor 

 subsidence indicated inside. 



1 " Vulkanologische Forschungen im ostlichen Zentralisland " : Neues 

 Jahrb., xxvi, Beilage-Band, p. 381, 1908. 



2 Peterm. Mitth., Band li, pp. 49-53, with map and crater-plans. 



