GEOGNOSY AND GEOLOGY. 119 
lands, are at a considerable height above the sea, as in the plateaux of 
Bavaria and Mexico. The same difference exists between the level of 
inland waters and that of the sea. Thus the surface of the Caspian Sea is 
about 31ft. below that of the ocean, and that of the Dead Sea about 1300ft. 
The bed of the Jordan, in part, lies below the level of the Mediterranean. 
This is unquestionably the case with the sea of Tiberias. Pl. 45, fig. 3, 
exhilits a section of Judea through the basin of the Dead Sea, from which 
these relations may be readily seen. In general, however, inland bodies 
of water are higher than the ocean, at times very much higher, as 
instanced by Lake Titicaca in Peru, existing at an elevation of 12,800ft. 
(pl. 45, fig. 12). The size of the lake or sea generally decreases 
with the elevation. 
5. The Interior of Mountains. 
We turn now to a brief consideration of the interior of mountains, after 
having thus examined the peculiarities of their external form. The simple 
fracture of a stone, of a naked rock, and especially mining operations, soon 
show us that the interior does not consist of a simple homogeneous mass ; 
on the contrary, we perceive that various rocks alternate with each other, 
and are split up into smaller parts of a great mass. We see cracks crossing 
through one another, and often in such a manner as to form subdivisions 
of definite form. These portions often exhibit a certain goniometrical 
character, comparable with crystallization, which comparison, however 
strictly speaking, is not allowable. If we consider the real character of a 
crystal, we shall soon find that no analogy exists between it and such a 
separating fragment, further than that of general external form, the edges, 
corners, and faces, not obeying strict crystallographical laws. The 
relative positions borne by these masses of separation or cleavage to each 
other are known as structure. 
6 Cleavage of Rocks. 
Masses of cleavages present themselves under two points of view, as 
angular and rounded. The latter are produced when the planes of cleavage 
return into themselves, these shelling off on further cleavage. Whether the 
cleavages be straight or curved, if they occur in one plane, this is called the 
plane of cleavage, which may extend over small spaces or through entire 
masses. The cleavage of rocks occurs in various degrees of complete- 
ness. The application of force is sometimes necessary to separate the 
cleavage masses, others are entirely separated, and in other cases, again, 
the spaces of separation are no inconsiderable cavities. In dealing with 
cleavage it is necessary to ascertain whether such be essential or 
non-essential; whether it stand in prime connexion with the character of 
the interior or not. The non-essential are entirely accidental, and are 
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