10-i General View of the Mode of Formation of Iceland. 



glomerates, or into beds of palagonite.* This is the mode 

 of the origin of the first trap-formation, and of its co-ordi- 

 nate bed of tufta. 



After such a catastrophe, months, and probably whole 

 years elapsed, before a second similar eruption followed. 

 Then a new fissure, either in the neighbourhood of the 

 former, or at a greater distance from it, again broke open 

 the volcanic furnace. If the place of the second eruption is 

 sufficiently removed from the first, there will not be the 

 slightest communication between the two recent foi-mations, 

 unless it be that the shower of ashes of the second erup- 

 tion has accidentally spread into the sphere of the former ; 

 if, on the other hand, the eruptive localities he at a small 

 distance from each other, the beds of tufi^a come in contact ; 

 the newer overlaps the older ; as also a new pai't of the 

 original bottom of the sea. There now follows a new sub- 

 marine palagonite and amygdaloidal formation, which in- 

 deed is similar to the former, except in a chronological point 

 of view. The veins, in so far as they belong to the same 

 system, proceed alongside each other in a pai-allel direction, 

 or cross each other under very acute angles ; their lateral 

 ramifications again unite and cross each other in different 

 storeys, so that the mere fact of being above or below is 

 here no criterion as to the age of the formations. 



While this secular rising of the land is going on, the se- 

 cond eruption also is followed by a new instantaneous rising. 

 After the lapse of some time, there occurs a third eruption, 

 which either stands quite isolated, or unites, in a manner si- 

 milar to that already described, with one or with both of the 

 former, and may receive into its tuffa fragments of the already 

 existing formations. A fourth eruption, and a fifth, and so 

 on, continually I'epeat the same process. Every time a new 

 bed of tuffa is formed, there arise new veins, new lateral ra- 

 mifications, and new instantaneous risings ; the sea over the 

 localities of eruption becomes always less and less deep, un- 

 til, at last, the bottom begins to rise above the level of the 

 sea in one or in several islands. 



Thus, have thousands of eruptions produced thousands of 



* This rock forms the basis of those tuffas named in Iceland mohera. 



