1870, J T. s. Huxr — ON granitic rocks. 403 



filling the resulting cavities, in wbicli he is forced to recognize 

 the intervention of water, though by no means admitting the 

 aqueous origin of veins, since he holds even those of quartz to 

 liave been formed by igneous injection. (Gcologie Lt/onnalsc^ 

 ='^■278. 



§ 2G, When we consider the cause which has produced the fis- 

 sures in the mica-schisis and gneisses of New England, which 

 hold the granitic veins already described, it is to be remarked 

 that their comparative abundance, their shortness and their ir- 

 regularity destinguish them from the fissures which are filled with 

 eruptive rocks. Examples of the latter maybe seen near Dan- 

 ville. Maine, where dykes of fine-grained dolerite are posterior to 

 the eudouenous granitic veins here occuring in the mica-schist. 

 These dykes may be supposed to be dependent upon movements 

 in the earth's crust opening deep fissures which connected with 

 some softened rock far below. Through such openings were ex- 

 travasated the exotic rocks, whether granites or dolerites, — more 

 or less homogeneous mixtures, often widely different in composition 

 from the encasing rocks. The endogenous veins, on the contrary, 

 are distinguished not only by their more or less heterogeneous and 

 often banded structure, but by the fact that their principal con- 

 stituents are the mineral species most common in the adjacent 

 strata. 



§ 27, A'^olgcr has attributed the formation of the openings 

 containing concretionary veins to the force of crystallization, which 

 is shown to be very great in the congelation of water and the 

 crystallizing of salts in cavities and fissures. Such a process once 

 commenced in an opening in a rock would, he conceived, be sufiicient 

 to make still wider the fissure, which might be fed by fresh solutions 

 passing by capillarity through the pores of the rock. If this 

 process were to become concentrated around several points, the 

 intermediate space might be so opened that free crystallization 

 could go on, resulting in the production of geodes in veins thus 

 formed. 



Fournet, on the other hand, suggests that contraction in the 

 cooling of erupted granites gave origin to the fissures and geodes 

 now filled or partially filled with crystalline minerals at Fariolo, 

 and we may readily suppose that a process of contraction attendant 

 upon the crystalline aggregation of the materials of sedimentarv 

 strata, would give rise to rifts or fissures therein. The lesions 

 thus produced in the solid rocks become more or less completely 



