374 REACTION OF THE INTERIOR OF THE EARTH 



could give us no information as to the general genetic 

 connection of the volcanoes in the basin of the Pacific. 

 It is otherwise when we confine our consideration to 

 single groups of islands, and go back in imagination to 

 the, perhaps, pre-historic epochs, when the many now 

 extinct linearly arranged craters of the Ladrones (Ma- 

 rianas), the New Hebrides, and Solomon's islands 

 were in a state of activity; but which craters we are 

 certainly not justified in assuming to have become suc- 

 cessively extinct one after another in any particular 

 geographical direction, as, for example, from south-east 

 to north-west, or from north to south. I have here 

 spoken of volcanic ranges of islands in the high seas, 

 but the same reasoning would apply to the Aleutian or 

 other "coast islands." Creneral conclusions respecting 

 the direction of a process of cooling are illusory, on 

 account of the influence on such cooling processes of 

 temporary obstruction or freedom from obstruction in 

 the channels of conduction. 



Mauna Loa, or Boa (or Mouna acording to the Eng- 

 lish mode of writing), which was found by a careful 

 measurement ( 509 ) of the American exploring expedition 

 under Captain Wilkes to be 13,758 feet high, or 1600 

 feet higher than the Peak of Teneriffe, is both the 

 greatest volcano in the Pacific, and also is the only one 

 still thoroughly active in the entire volcanic archipelago 

 of the Hawaii or Sandwich islands. The summit-craters, 

 of which the largest is about 13,000 feet in diameter, 

 present in their ordinary .state a solid floor of cooled 

 lava and scoriae from which rise small cones of eruption 

 exhaling vapours. The summit-openings are in general 

 but little active; but in June 1832, and in January 1843, 



