General Fietv of the Mode of Formation of Iceland. 105 



different beds of trap, of palagonite, and of amygdaloidal tuffa, 

 and equally numerous instantaneous risings, and contributed, 

 during immense intervals of time, towards the formation of 

 the island of Iceland. From this mode of explanation, we 

 may understand how the innumerable varieties of dissimilar 

 trap and tuffa have arisen, how the later formations can con- 

 tain fi'agments of the former ones, and how the veins cross 

 certain beds of palagonite, without our being constrained to 

 the conclusion that a universal covering of palagonite forms 

 the base of the whole island, whilst we cannot comprehend 

 how this palagonite has itself arisen, and whence its materials 

 are derived. 



After the beds of tuffa, together with the different trap 

 foi'mations, had assumed a certain extension, the trachytic 

 rocks of the same kind broke out here and there into veins, 

 through the already extensive volcanic covering of the bot- 

 tom of the sea, in the very same way as the traps themselves 

 had done. These trachytic veins passed through the traps 

 and tuffas with which they met, and caused in them new in- 

 stantaneous risings. The trachytes were again followed by 

 other trap injections, which passed through them, raised them 

 up, and spread through them in vein-shaped lateral ramifica- 

 tions. Thus simple is the explanation of the phenomena 

 which we have formerly described among traps and trachytes, 

 and their mutual injections into each other. After this al- 

 ternate process had continued for many thousand years, Ice- 

 land had again received a new and considerable increase, and 

 it began to assume a greater size. 



Plants gradually covered the surface of the island, the val- 

 leys became covered with gi'ass and moss, and there were 

 also found extensive forests, which, as yet, had nought to 

 fear from the stroke of the axe. The smaller hills were not 

 yet covered with glaciers, and thus the climate, favoured by 

 the superior influence of the ocean, was milder than in our 

 days. Whole generations of trees arose and perished, tliey 

 were the silent witnesses of countless new eruptions, which 

 broke out, either whilst under the sea, or after the mainland 

 had been formed, accompanied by earthquakes, and by showers 

 of scoria, ashes, and incandescent lavas. The forests sank 



