142 The Distribution of paet i. 



in the sea, or near its shores. This fact of the ocean- 

 islands being so generally volcanic is also interesting 

 in relation to the nature of the mountain-chains on 

 our continents, which are comparatively seldom vol- 

 canic ; and yet we are led to suppose that where our 

 continents now stand an ocean once extended. Do 

 volcanic eruptions, we may ask, reach the surface more 

 readily through fissures formed during the first stages 

 of the conversion of the bed of the ocean into a tract 

 of land ? 



Looking at the charts of the numerous volcanic 

 archipelagos, we see that the islands are generally 

 arranged either in single, double, or triple rows, in 

 lines which are frequently curved in a slight degree. 1 

 Each separate island is either rounded, or more gene- 

 rally elongated in the same direction with the group 

 in which it stands, but sometimes transversely to it. 

 Some of the groups which are not much elongated 

 present little symmetry in their forms ; M. Yirlet 2 

 states that this is the case with the Grecian Archi- 

 pelago : in such groups I suspect (for I am aware how 

 easy it is to deceive oneself on these points), that the 

 vents are generally arranged on one line, or on a set 

 of short parallel lines, intersecting at nearly right 

 angles another line, or set of lines. The Galapagos 

 Archipelago offers an example of this structure, for 

 most of the islands and the chief orifices on the largest 

 island are so grouped as to fall on a set of lines ranging 

 about NTV. by 1ST., and on another set ranging about 

 WSTV. : in the Canary Archipelago we have a simpler 

 structure of the same kind : in the Cape de Verde 



1 Professors "William and Henry Darwin Rogers have lately in- 

 sisted much, in a memoir read before the American Association, on 

 the regularly curved lines of elevation in parts of the Appalachian 

 range. 



2 ' Bulletin de la Soc. Geolog. torn. iii. p. 110. 



