Relations of Continental Masses to Oceanic Basins. 467 
earth, and at various times in its history, have been formed. 
Such movements are called orogenic movements. No sooner are 
mountain masses formed than they begin to be wasted away 
by surficial, or epigenic, forces. In many regions mountain 
ranges have arisen and fallen several times during the history 
of the earth. The molecular movements of the rocks 
may affect the shape and arrangement of their constituent par¬ 
ticles, or the very composition of the particles themselves may 
be changed. As a result the character and structure of the 
rock masses affected may be wholly altered, and even under 
quiescent mechanical conditions the solid rocks beneath our feet 
may be so changed as not to contain one trace of the original 
minerals composing them. 
It is the purpose of this paper to inquire into the character 
and effects of these various earth movements. 
Relations of Continental Masses to Oceanic Basins . 1 —Before con¬ 
sidering the earth movements it is necessary to recall the relations 
of the continental masses to the oceanic basins. The bed of the great 
world ocean is for the most part a continuous plain, surpassing 
in evenness, as it does in extent, any plain upon the continental 
masses. Below the general level of the plain are smaller areas 
called deeps, such as the Tuscarora Deep. In most 
cases the passage from one level to the other is very gradual. 
Above some of these deeps are 30,000 feet of water. One may 
imagine himself on the floor of the vast ocean plain, traveling 
toward the continental area. As he nears the continental mass 
a gentle but great slope rises before him. Climbing this slope* 
which places him 14,000 feet farther from the center of the earth 
than when on the ocean bed, he finds himself upon another plain* 
less even than the first, being broken by mountain ranges and other 
irregularities. This plain is the world continent. When this 
upper plain is reached he may still be 100 or 150 miles from the 
border of the continent as we ordinarily think of it, for the 
great land masses are fringed by shallows varying from a few 
miles to 150 miles in width. The lands below these shallows belong 
1 On the height of the land and the depth of the ocean, by John Murray: 
Scottish Geog. Mag., Vol. IV, 1888, pp. 1-41. 
