66 BUNSEN ON THE FORMATION OF 



lofty perpendicular cliffs of the mountains on the coast, con- 

 sisting chiefly of pyroxenic substance, furnishes a distinct picture 

 of this stupendous metamorphism. Trap dykes of more than a 

 thousand feet in height are not unfrequently seen there tra- 

 versing the entire rocks, sometimes massive, sometimes stra- 

 tified, and branching out through the enormous horizontally 

 extended trap beds in such a way as to leave not the slightest 

 doubt that these masses, intersecting and covering the tuff 

 rocks, are no other than the product of melted matter which 

 was erupted through these dykes. The results of the igneous 

 action of these injected beds of trap stand in a most intimate 

 relation to the magnitude of the heating and heated beds, when 

 especial influences have not prevailed to modify them. 



In the amygdaloid rocks resulting from the metamorphism of 

 tuff beds, whose original aggregation may frequently be di- 

 stinctly enough recognized in the sometimes angular, sometimes 

 rounded, imbedded masses, such a gradual transition into the 

 unaltered trap rocks may in some instances be traced, that there 

 is an absolute want of any line of demarcation between the two. 

 The passage of a crumbling hydrated rock into one which is 

 perfectly anhydrous, with all those characteristic stages of zeo- 

 lite formation presented by a fragment of ignited palagonite, may 

 here be observed on a large scale. It consequently cannot admit 

 of a doubt that it was neither neptunian nor plutonic agencies 

 alone which gave rise to the formation of zeolitic rocks in Ice- 

 land. On the contrary, we have here to do with a long series 

 of different phases of metamorphic development, the products 

 of which present themselves in the amygdaloid rocks. A truly 

 plutonic rock possessing a superbasic composition, suffers a 

 neptunian metamorphism into palagonite and palagonitic tuff, 

 either at the place of its original eruption, or during the trans- 

 port of its mechanically broken fragments. New plutonic masses 

 break through this altered rock frequently after a long period of 

 rest, and by a second act of metamorphism, now plutonic, con- 

 vert it into zeolitic amygdaloid. Finally, a third neptunian 

 metamorphosis, caused by gaseous exhalations and aqueous va- 

 pour, results from this change, and of which, as the last stage of 

 all these processes, I shall speak subsequently. However simple 

 and inteUigible these phaenomena may be as regards the forma- 



