FOKEIGN CORRESPONDENCE. 
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The metainorphism of the eruptive rock (wliatever be its nature) is 
generally less characteristic than that of the strata uplifted. M. 
Delesse thinks this is easy to account for, as the latter were solid at 
the time the phenomenon took place, and consequently not in a con- 
dition to exercise a reaction upon tiie plutonic rock. This is, how- 
ever, an insufficient reason, and M.Delesse's own observations show that 
even where no change or metamorphism is apparent in the ujilifting rock, 
a few simple tests will enable us to affirm that a change has leally taken 
place. When the plutonic rock is examined comparatively (in a large 
vein, for instance) at its borders and at its centre, it is remarked to 
have undergone a modification, not only in its structure, but also in 
its composition. Such modifications do not, howevei', extend more 
than a few inches from the borders ; they are more marked in smaller 
veins, and more visible iu lava and ti'aps tliau in granite rocks. 
Near the borders of a vein of rock its structure has become schistose, 
prismatic, granular, amygdaloidal, &c., according to circumstances. 
The density of the rock has diminished in these parts, and this is 
very notable in the case of ti'ap-rocks. The quantity of water which 
it contains has, on the contrary, augmented.* In some cases struc- 
ture alone has been modified ; but in most the composition of the rock 
is changed also. Sometimes this composition is exactly intermediate 
between that of the uplifting and that of the upheaved rock. 
Among the minerals found in the eruptive rock near the parts iu 
contact with the uplifted strata, M. Delesse indicates carbonates and 
quartz ; also, different silicates, principally garnet, idocrase, and 
epidote. But when the reaction that has taken place between the two 
rocks has been very active, a complete exchange or mixture of ele- 
ments has been operated. 
Metalliferous lodes are often seen either in the uplifted or in the 
plutonic rock. They penetrate both, and are most abundant at the 
points of contact. 
As concerns minerals produced during metamorphism by contact, 
they are very numerous, as we have already shown in our preceding 
papers, and they are much the same for the plutonic rock and the 
strata which it has uplifted. In numerous cases these minerals have 
been formed from the elements of the one and the other. Quartz and 
spathic carbonates are very frequent where either the eruptive rock 
or the other contains silica and carbonates. Zeolites are more espe- 
cially associated with volcanic rocks, such as lava, basalt, and trap. 
Tourmaline, with granitic rocks. The numerous silicates for which 
M. Dana formerly established the types garnet and pyroxene have 
been formed in the eruptive rock, and in the uplifted strata. 
M. Charles Martins, the eminent botanist of Montpellier, informs 
us that he has discovered, among some notes taken diu'iug several 
scientific excursions made by him at different times, a striking proof 
of the correctness of a theory he propounded some time ago to esta- 
* This is probably one of the cliief causes of the diminution of specific gravity. 
