Massive Crystalline Mocks. 113 



made one way or the other. As has often happened in the case of 

 granitic rocks, and even granular limestone, the fused or plastic 

 material, under the pressure attending the subterranean movements, 

 would have entered and. filled all fissures that might have been 

 opened to it, and so have made veins or dykes having the sizes of the 

 fissures, whether large or small, and possessing also a uniformity 

 of grain like that of ordinary erupted rocks.^ 



(2) Again, whatever the process of ejection, fragments, large or 

 small, of any rocks adjoining such fissures might have become in- 

 cluded in the fused or plastic material. 



(3) Moreover, the contact-phenomena in the case of veins so 

 formed maj^ be as decided and extensive as in that of any dykes 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 move- 

 ment, 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 metamoi'phism, 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 ordinary erupted rocks are nothing but 

 fused sedimentary rocks need not be here discussed. The improba- 

 bility of the view comes from the improbability of any movements 

 in the earth's crust being sufficient to fuse its own rocks or the over- 

 lying sediments. But the epochs of metamoi'phism are the times 

 not only of the profoundest movements of the crust, but also of the 

 most thoi'ough 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 fissui'es of 

 any rock so fused might have any extent, even that of the whole 

 depth of the rocks metamorphosed; for the fissures 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 fissure. 



But while there may be these resemblances between the efi'ects of 

 metamorphism and those of deep-seated eruption, 



b. The results of fusion of sedimentary beds under metamorpJiic 

 action may have distinguishing peculiarities. — First: The kinds of 

 rocks so resulting are likely to vary greatly at comparatively short 

 intervals, because sedimentary beds often vary thus. They should 

 not have that uniformity for scores or hundreds of square miles 



1 In the writer's Manual of Geology (1880), veins of this kind are called veins of 

 plastic injection, an abbreviation of the full statement that they were made by the 

 injection of material rendered plastic or fused dui'iug a process of metamorphism. 

 They are better called dyke-like veins. 



DECADE II. — VOL. VIII. NO. III. 8 



