* 
436 PACIFIC OCEAN. 
III. Fissures and displacements of the crust, owing to the contraction below it drawing 
it down into a smaller and smaller arc ; also, from a change in the earth’s oblateness. 
a. Fissures influenced in direction by the structure of the earth’s crust,—because of the 
existence of such a structure, and also because the tension causing fractures would be exerted 
with some reference to the structural lines, the tension and the structure being both simulta- 
neous consequences of cooling. 
b. Direction of fissures modified by the relative positions of the large areas of unequal con- 
traction, and whatever the actual course, frequently attended by transverse fractures. 
c. As the force of tension acts tangentially in a great degree, (like the pressure of stone 
against stone in an arch, and that of the whole arch against the supporting or confining abut- 
ments), the effects will appear either over the subsiding area, or on its borders; and they will 
be confined to the latter position whenever the surface is strong enough to resist fracture. 
d. The borders of large subsiding areas sooner or later experiencing deep fissurings and 
extensive upliftings through the tension or horizontal force of the subsiding crust; these uplift- 
ings frequently in parallel series, of successive formation, or constituting a series of immense 
parallel folds ; that side of the fold in general steepest which is most remote from the sub- 
siding area. 
e. Fissures formed having the character of a series of linear rents either in interrupted lines 
or parallel ranges, instead of being single unbroken lines of great length, and this owing to 
the brittle nature and structure of the earth’s crust; ranges sometimes curved, either from 
having a general conformity to the outlines of contracting areas, or because proceeding from 
an inequality of force along parallel lines of tension over a subsiding area. 
IV. Escape of heat and eruptions of melted matter from below through opened fissures, 
a. Igneous ejection of dikes an effect and not a cause of displacements. 
b. Some points in the wider fissures continuing open as vents of eruption. The outlines of 
large contracting areas being liable, from the cause just stated, to deep fissurings, these there- 
fore likely to abound most in volcanic vents. 
c. Heat from many fissures giving origin to hot springs. 
d. Distribution of the heat attending submarine action, causing metamorphic changes. 
V. Earthquakes, or a vibration of the earth’s crust, consequent on a rupture, internal 
or external, and causing vibrations of the sea besides other effects. 
VI. Epochs in geological history. 
VII. Courses of mountains and coast lines, and general form of continents, determined 
to a great extent by the general direction ‘of the earth’s cleavage structure, and the posi- 
tion of the large areas of greatest contraction, 
Thus the existence of continental areas determined the existence of the mountains they 
contain ; and also the mountains in their turn determined to some extent the position and 
nature of subsequent deposits formed around them, effecting this either directly, or by 
influencing the courses of ocean currents during partial or entire submergences, or by 
determining the outlines of ancient seas of different epochs. According to this view, the 
general forms of continents, and those of the intermediate oceanic depressions, however 
modified afterward, were to a great extent fixed in the earliest periods by the condition 
and nature of the earth’s crust. ‘They have had their laws of growth, involving conse- 
quent features, as much as organic structures, 
