112 Frof. J. D. Dana — Mefamorphism of 



infiltration or segregation, that is, they are not due to the filling of 

 fissures by material supplied slowly in solution or vapour ; for no 

 difference in coarseness of texture or structure exists between the 

 rock constituting them and that of the massive rock elsewhere ; 

 they are just such as have been made by simple injection. 



There are also peculiarities in the exterior of inclusions, and in 

 the walls of veins or dykes, in some cases, which favour the idea of 

 fusion. At Verplanck, the limestone of the w^all is often discoloured 

 for two or three inches, and sometimes penetrated by the material of 

 the vein, or contains minute crystals of hornblende ; and in other 

 cases, the limestone is impregnated with the hornblendic or augitic 

 material in irregular lines or bands, so that surface erosion has left a 

 complexity of small curving ridges. The crystallization of the lime- 

 stone adjoining the vein is sometimes coarser than elsewhere ; though, 

 in general, no difference is apparent. On a small point, just north 

 of the region of veins, part of the limestone is of the coarsest kind, 

 the crystalline grains over a fourth of an inch broad, while the larger 

 part is very fine in grain, like the most of the Verplanck limestone 

 — a fact that indicates the local action of escaping heat. 



Still more positive evidence, if possible, of fusion is shown at the 

 junction of the schists of Cruger's Point with the soda-granite, where 

 the schist itself bears evidence of partial fusion and exhibits other 

 contact-phenomena. 



The proof of the crystallization of the rocks from a more or less 

 perfect state of fusion or plasticity is thus complete. 



2. Evidences as to Condition of Fusion. 



But, admitting fusion or a plastic condition, the question still 

 remains : 



Were these once-fused rocks fused approximately in situ, that is, 

 where, or near where, they now lie ; or were they erupted through 

 fissures from great depths below ? that is, using Dr. Hunt's terms, 

 are they indigenous, or are they exotic ? 



a. The results are partly tlie same wliicliever the condition of fusion. 

 — If they were fused where approximately they now lie, that fusion 

 must have come from accessions of heat, and such accessions may 

 have resulted from the movement and friction connected with an up- 

 turning of the rocks ; and it may hence have been one of the results, 

 in that region, of metamorphic action at an epoch of general mefa- 

 morphism ; and if so, at the very time that these rocks became fused 

 or plastic through the process, other rocks of the region, owing to 

 less extreme metamorphic action, or to less fusibility, may have been 

 left with their bedding unobliterated ; just as much granite in New 

 England and other countries received its crystalline condition in the 

 same process and at the same time with the associated schistose 

 rocks, the gneisses, mica-schists, etc. 



All the facts as to fusion which have been presented are consis- 

 tent with either mode of origin, even to the inclusions and the dykes 

 or veins. 



(1) The veins or dykes have the same essential characters whether 



