ON CHANGES OF LEVEL IN THE PACIFIC OCEAN. 137 



From the surface of Mount Loa we learn that the occurrence 

 of beds of lava with ropy lines characterizing the surface (pro- 

 duced by the flowing of the lava) indicates a subaerial origin. 

 In ejections beneath the sea, the surface of the lava is so acted 

 upon by the cold water that such lines are not preserved. From 

 these indications we ascertain that Tahiti, Upolu, Savaii, Oahu, 

 Maui, and Kauai were nearly at their present height when the 

 latest eruptions took place. 



We learn again from Mount Loa, that a subaerial origin is 

 shown by a great number of lateral cones of lava or cinders. The 

 absence of these small cones from Tahiti cannot, however prove 

 the contrary ; since the island has been subject to extensive de- 

 nudation, and these minor craters would be the first parts to dis- 

 appear. Western Maui, as well as the larger part of Kauai, re- 

 sembles Tahiti. On Eastern Maui and Savaii these lateral cones 

 are still numerous, and the surface of these lands bears evidence 

 of recent subaerial fires, and little denudation. 



The cavernous nature of Mount Loa, is another point that may 

 be looked upon as proof of subaerial origin ; and it is conclusive 

 upon this point, as far as regards the exterior coating of Mount 

 Loa, the only part exposed to view. Like the two preceding 

 kinds of evidence, it is of very difficult application. In Eastern 

 Oahu, however, in the lower slopes beyond Diamond Hill, there 

 are many caverns so similar to those of Mount Loa, that they 

 clearly evince that the land was above water when the ejections 

 took place. 



The recent ejected rocks of Mount Loa, though often very 

 compact, still contain some ragged cellules; and this kind of cel- 

 lule rather than the absence of them altogether is a good proof 

 of the rocks cooling without pressure above. The application 

 of this test leads us to no different results from those already 

 stated. 



We arrive, therefore, at the conclusion that while it is apparent 

 that the latest eruptions of many of the Pacific islands were sub- 

 aerial, and the most of these lands were at a much lower level in 

 the course of their progress, we cannot point out which were of 

 submarine origin ; and of course we learn nothing with regard 

 to the earliest condition of these centres of eruption, from exam- 

 ining the rocks above the present sea level. 



The action of the sea on the cliffs of the islands before these 

 shores were protected by reefs, is another source of evidence with 

 regard to the level of the land at an early epoch. Such facts are 

 very difficult to be identified ; and we have distinguished only a 

 single undoubted case. This occurs on the north side of Vanua 

 Lebu, one of the Feejees. 



The island of Mali upon this coast is, in fact, two islands : they 

 are separated by a narrow passage, and stand but a short distance 



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