326 TEE BOTTOM OF THE SKA. 



1. That the lava cools more uniformly, and extends 

 lurther upon a plane surface. 



2. That a submarine volcano ejects a less quantity 

 of conglomerate, or of fragmentary matter, than a 

 subaerial one, or that its igneous product extends 

 further, and stratifies in thinner sheets of con- 

 temporary lava, than is the case with that of other 

 volcanoes. 



If these opinions be correct, the regions where 

 we find immense formations, sometimes slightly in- 

 clined, of traprock and basalt, to which some coun- 

 tries are indebted for their picturesque aspect, have 

 been at some distant period submerged, and exposed 

 to the action of a submarine volcano, which has 

 covered them with its products. 



In such cases, when the volcano is in repose, 

 it is obvious that submarine deposits of every kind 

 — including animals and plants, if the depth be 

 not too great — will be found superimposed upon 

 the lava. Accordingly, when the ocean-bed is 

 upheaved to the light of day, we find a sheet of 

 basalt between two beds formed of the debris of 

 marine animals. 



In Iceland we find subaerial volcanoes side by 

 side with others of submarine origin, the latter 

 having been upheaved to the light of day long after 

 their activitv had ceased. The first are the Jokuls, 



