E. B. Bailey — Iceland, a Stepping -Stone. 473 



stated that the oceanic basins of the earth originate and increase 

 through subsidence and inbreak, Suess turns his attention to the 

 " seas" and craters of the moon, and suggests that Iceland with its 

 ring-fractures and cauldron-subsidences may furnish us with a true 

 conception of the lunar surface (p. 598). He develops this com- 

 parison in some detail, and then passes on, as one might expect, to 

 Southern Italy, and claims the Calabrian earthquakes as marking the 

 growth of a caldera of lunar type under our very eyes, with the 

 Lipari volcanoes at its centre and Etna on its periphery. 



Suess also refers (p. 595) to a well-known tendency of major 

 craters of the moon to carry minor craters "riding" upon their 

 margin — as Etna may be said to ride upon the Calabrian cicatrice. 

 He suggests that this riding on the ancient rampart may be 

 accounted for as a result of peripheral fissuring. His terrestrial 

 analogues he derives from Italy; but, had he known, he might have 

 pointed once more to Iceland, to the rim-craters of the Askja 

 Caldera; or he might have invoked the aid of Scotland, and 

 interpreted the riding craters as the surface manifestation of ring- 

 dykes of the kind now known to occur at Glen Coe, Etive, Ben 

 Nevis, and Mull. 1 



It appears from what Suess says that he had no hesitation in 

 classifying together cauldron-subsidences of the most diverse 

 dimensions. On the one hand, he compares the cauldron-subsidences 

 of Iceland with certain sinkings which have followed in mining- 

 districts upon the extraction of salt, or the draining of a substratum 

 of quicksand (p. 264) ; on the other hand, he links them with lunar 

 craters and with depressions of oceanic extent, whether lunar or 

 terrestrial — although admittedly with increased extent the circular 

 form tends to disappear (p. 598). 



This grouping of large and small may be quite mistaken, but it is 

 likely to be accorded a very general sympathy. The most diminutive 

 of the phenomena chosen by Suess for comparison is a series of 

 arcuate fissures found by him in an asphalt pavement which was 

 sinking differentially as compared with its curbstone (p. 503). 

 " The subsidences of the asphalt pavement take place," he says, " on 

 the concave side of each of the several arcuate fragments. ... A 

 similar process seems to have occurred in the north-west of Iceland." 

 One should not forget, however, that important exceptions are 

 afforded along the western margin of New Iceland, where 

 Thoroddsen finds the downthrow on the convex, and not the concave, 

 side of the boundary faults. 



Leaving Suess for a minute it may perhaps be profitable to draw 

 attention to other instances of what appear to be ring-fractures on 

 a small scale. About 3 per cent of the older cracked picture 

 surfaces of a collection such as that of the National Gallery in 



1 The investigation of these occurrences has been among the happy duties 

 of the Scottish Geological Survey. Those mainly employed on the work have 

 been H. B. Maufe, C. T. Clough, H. Kynaston, W. B. Wright, J. E. Bichey, 

 and myself. Many of our results are given in two Survey publications, The 

 Geology of Ben Nevis and' Glen Coe (1916) and Summary of Progress for 

 1914 (1915). 



