204 J. D. Dana—Geological Relations of the 
(3) Moreover, the contact-phenomena in the case of veins so 
formed may be as decided and extensive as in that of any 
dikes or erupted masses. 
(4) Further, the evidences of fluidal movement exhibited in 
the broken condition of many of the crystalline grains would 
be the same. Such a fragmenting of grains taking place after 
the stiffening of incipient solidification requires but a moderate 
amount of movement, and this is all that such circumstances 
would admit of One foot would suffice; thousands would 
be impossible. 
(5) Again, the resulting rocks need not, and generally do 
not, differ in kinds from erupted rocks of deeper source. In 
such fusions in the course of a process of metamorphism, the 
thickness of the rocks undergoing common movement may 
have a depth of 20,000 feet or more, and the fusion, therefore, 
would not be superficial. The view that many of the ordi 
nary erupted rocks are nothing but fused sedimentary rocks 
need not be here discussed. The improbability of the view 
comes from the improbability of any movements in the earth’s 
crust being sufficient to fuse its own rocks or the overlying 
iments. But the epochs of metamorphism are the times 
not only of the profoundest movements of the crust, but also 
of the most thorough upturning of sedimentary beds, and if 
these are ever melted through the friction of upturning, or by 
its aid, then would be the occasion for it. 
(6) Veins made at such an epoch by the injection into fis- 
sures of any rock so fused might have any extent, even that 
of the whole depth of the rocks metamorphosed ; for the fis- 
sures may be thus deep. And the material filling them, since 
it might be that of the bottom rocks, might be wholly unlike 
that of the rock on either side of all the higher parts of the 
dreds of square miles which often characterizes ejections that 
have come up from regions beneath the supercrust." Sedi- 
ments, and therefore sedimentary deposits, are liable to fre- 
yi and sudden changes as to material, which igneous out- 
ows cannot imitate. Secondly, the rocks are likely to have no 
3 The term supercrust is used for that part of the earth’s crust which has 
been made by sedimentation, the true crust being restricted to the part beneath 
which is a result simply of cooling, 
ae 
