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



London show very well-defined groups of circular fractures. They 

 occur in concentric systems side by side with the more usual 

 irregular cracks of the type known to geologists as suncracks — from 

 their frequent development in drying clay. Circular fractures play 

 a much greater role in the general crack system of less carefully 

 guarded canvases. In fact, almost every out-of-door painted canvas, 

 or linoleum, carrying a notice or advertisement, or stretched to cover 

 a tradesman's cart, shows circular fractures at one place or other of 

 its surface. Perhaps these fractures are analogous to the circular 

 cracks of a broken pane of glass, and in any case great care should 

 be taken in their interpretation. Indeed, they may not deserve the 

 name of ring-fracture at all. A ring-fracture in geology follows 

 a more or less cylindrical surface, and it should be remembered that 

 quite other fractures, better styled cone-fractures, have an equally 

 marked tendency to arcuate outcrop. Cone-fractures are now well 

 known through Harker's work on the inclined sheet system of Skye 

 and the later researches of others on the analogous systems of Mull. 

 But returning from this digression, let us recall the most numerous 

 ring-fractures of recent times. They originated in concentric 

 systems within and about shell-craters, when the impalpable dust of 

 the inner slopes contracted, and no doubt at its lower levels flowed, 

 after its first wetting by a shower of rain. 



The occurrence of arcuate volcanic fractures in Iceland, sometimes 

 with a great radius of curvature and determining the site of major 

 volcanoes, seems to lead naturally to a comparison with other volcanic 

 arcs such as that of the Aleutian Isles. But Suess does not follow 

 this line of approach. For him Icelandic arcs are a phenomenon of 

 subsidence, whereas the mountain arcs, with which he classes the 

 Aleutian Isles, are a phenomenon of lateral compression. I venture 

 to think that if he had lived much longer he would have claimed 

 a community of origin for the two systems of arcs. His ideas in this 

 connexion seem to have been undergoing evolution as he wrote. 



Early in his scientific career Suess started out to study the 

 development of the Alps. He travelled far, and, though outstripped 

 as time went on by certain of his comrades, he had good reason to be 

 content. He could afford to let others struggle on towards the 

 coveted summits of Alpine interpretation, while he lingered at a lower 

 level; for he had learnt to use the writings of others as an 

 astronomer uses a telescope, and through them to gaze upon the face 

 of the earth from chosen vantage points, and thus to enrich two 

 generations of geologists with a wisdom and knowledge gathered from 

 every corner of the globe. 



It is not surprising that at first he should regard the arcuate form 

 of the Alps as a combined result of push and obstruction. Nor is it 

 surprising that at first he should think of the Alps as typical of the 

 other arcuate chains of the earth's surface, and extend his conception 

 of push and obstruction to account for the configuration of the whole 

 class. 



If, like Darwin, he had learnt his geology on the borders of the 

 Pacific Ocean he might well have had quite a different outlook in this 

 particular. And as it is he seems to have turned increasingly to the 



