Vol. 59.] 



BOULDEli-CLAY IN ICELAND. 



357 



country, is built up chiefly of palagonitic tuffs and breccias, con- 

 glomerates (in part probably fluvio-glacial), and moraines. But, 

 while in other parts of Iceland the rule is that, owing to subsi- 

 dence, the basement of the breccia-formation has been hidden from 

 view, in Sngefellsnes, on the contrary, the basaltic basement of the 

 breccias, etc., can very commonly be seen. 



The Tertiary basalts of the peninsula, however, are also traversed 

 by faults and very clearly have subsided ; and in the eastern portion 

 of the cliffs of Olafsvikur-enni — a basal part of the great volcanic 

 pile of Snasfellsjokull (4710 feet) — the ' fundamental basalt ' has 

 even disappeared below sea-level, while farther west it again appears, 

 reaching however barely to a height of 100 feet above the sea. 



Now, the basement-layer of the breccia-formation is seen in 

 many places to consist of a greyish, indurated ground-moraine, 

 varying in thickness, and containing glaciated basaltic blocks of all 

 sizes up to 6 feet or more in diameter. Thus in the above-mentioned 

 cliffs of Olafsvikur-enni, the fundamental basalt is succeeded above 

 by an indurated ground-moraine, which in turn is overlain by a 

 thickness of probably more than 1000 feet of tuffs, breccias, con- 

 glomerates, and probably also morainic deposits. 



It is more profitable, however, to turn to the plateau of Mavahlid, 

 which projects in the promontory of Biilandshofdi. Here the escarp- 

 ment can be scaled in several places, and every single layer of a 

 section examined. The following diagram from the western face 

 of the escarpment may perhaps be taken to represent the normal 

 mode of composition of this plateau (fig. 1). 



Fig. 1. — Section of the plateau of Mavahlicl. 



g= Volcanic tuffs and breccias. 



f= Indurated ground-moraine, with 



striated stones, 30 feet. 

 e=. Columnar basalt. 

 cl— Conglomerate, about 40 feet. 

 c — Tufaceous sandstone, 20 to 30 feet. 

 b== Indurated ground - moraine, 



about 40 feet. 

 a = Fundamental basalt, reaching to 



about 400 feet above the sea. 



The fundamental basalt (a) differs in colour, in texture, and in its 



