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RICHTHOFEN — NATURAL SYSTEM 
The entire belt, composed of these three zones, has to be considered as one great 
area of elevation, characterized, at the same time, over its greater portion, by the rem- 
nants of the eruptive activity of the volcanic era. No portion of it, however, has, as 
we mentioned before, experienced an amount of additional elevation during that period 
equal to that of those mountain ranges which existed before it, and among which the 
Alps and Himalaya are the most prominent. In these cases there cannot have been any 
connection between the elevation and the ejection of the rocks to the surface, because 
these do not occur. But this does not preclude the connection between the elevation 
and those agencies which are the causes of eruption. It has been often demon- 
strated that the changes of level must have been accompanied by the formation of 
such fractures as would be closed next to the surface, and, though allowing of an in- 
trusion of plastic matter from below, would prevent its extrusion to the surface. It is 
probable that fissures of this kind may have been chiefly formed where high mountain 
chains are composed of metamorphic rocks, since they frequently exhibit vertical disloca- 
tions, partly parallel to their axis, and partly at right angles to it, by which the strata 
on one side have been moved thousands of feet above the other, and which, notwith- 
standing, did not give vent to the ejection of rocks. These faulting fissures appear to 
form frequently the lateral boundaries of mountain ranges and the limits of the mani- 
festation of vulcanism, and both these circumstances allow us to infer that they extend 
downward to great depth. Though one of the main features in the geological 
structure of the Alps, they have hitherto been little examined. But itis probable that 
their formation was coincident in time with the main phase of elevation, that is, 
with the volcanic era. if, then, in that part of the crust over which the Alps are ele- 
vated, such fractures were formed as did not open on the surface, then all the agen- 
cies below would codperate towards elevation alone. The expansive force produced 
by aqueous fusion would find no vent for the discharge of the masses by which the 
volume had increased, nor would there be any opportunity given for the escape of 
heat by hot water and other means; while, on the other hand, the masses in depth 
would be relieved from pressure by the formation of this kind of fractures in the same 
way as by those which would allow the passage of liquid matter to the surface. In the 
case of the latter, an immense amount of force is spent in other modes of action, while 
in the first case it could be applied almost exclusively to elevation. Besides this direct 
action, however, we must also keep in view, that in those regions where fissures would 
not be open at the surface, the conditions required for metamorphic action would be 
given on a particularly grand scale. Gases and water would not reach the surface, but 
be employed in depth in promoting metamorphic action over vast regions, and imcreas- 
ing the rate” of elevation. It may be by processes of this kind that already in ancient 
times, contemporaneously with an accelerated elevation, were formed those granitic 
wedges surrounded by broad belts of foliated metamorphic rocks, which are peculiar 
to certain mountain ranges, particularly to those which also in the voleanic era have not 
been the theater of eruptive activity. The intrusion, from below, of heated masses into 
fissures closed towards the surface, would give all the conditions required for the exhibi- 
tion, on a grand seale, of those processes of hydropyric metamorphism which Daubrée 
has rendered probable by his experiments and theoretical deductions. 
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