TOPOGRAPHICAL FEATURES. A15 
1. Ruptures seldom continuous at the surface for long distances, and 
usually consisting of a series of rents ; the rents often largest at one 
extremity.—It has heretofore seemed the most natural supposition that 
a long linear group of islands like the Hawaiian chain, should have 
occupied the site of a single uninterrupted fissure, and this view is 
often implied by writers treating of the origin of chains of islands as 
well as ranges of mountains. ‘That it is a gratuitous assumption it is 
needless to assert; and moreover it is obvious from the various 
courses and irregularities in a single mountain range that it cannot 
be always true. The facts in the Hawaiian Islands prove that the 
group originated in a series of rents; for they show that for several of 
the islands the fissure was largest towards the southeast part of the 
island, where the fires were longest in action, a fact which could not 
be comprehended if we admit only a single fissure for the group, and 
is perfectly compatible with the idea that there wasa number of them. 
This is farther confirmed by the fact that the subordinate rents 
correspond in character with the series as a whole, the southeast por- 
tion of the series, as well as of the separate islands, bearing evidence 
of having been the part where the widest rupturing took place 
(page 281). 
From the nature of the earth’s crust—a brittle material, of some- 
what uneven texture and probably also of unequal thickness,—we 
should infer that its fractures would be a series of rents rather than 
a continued straight line of rupture. For the latter would require an 
even application of force, upon a material of very regular structure 
and uniform texture,—a condition of infinite improbability as regards 
the earth. 
Whatever the force causing rupture, we learn from actual facts, 
and especially from the progress and effects of earthquakes, that this 
power has its point or region of maximum effect, from which, along 
some determinate line, it gradually diminishes, or towards which it 
gradually increases. And this condition, and the others alluded to, 
would necessarily produce the result so well exemplified in the 
Hawaiian Group. 
Another example of fires dying out at an extremity of a group has 
been found in the Samoan Islands: we have, therefore, the same 
evidence here, that the ruptures which originated the group were 
largest towards one extremity. This extremity is the western in 
Samoa, and therefore the force instead of being greatest to the south- 
east, as in the case of the Hawaiian chain, was here greatest to the 
northwest. 
