Pyroxenes. 19 



line of reasoning would also be favored by the common explanation 

 of infiltrated veins which have been "locked." 



Finally I would say that there seems to me to be the best of 

 reasons for discarding the explanation ordinarily adopted in all cases, 

 namely, by corrosion or by imperfect crystallization, a worse explan- 

 ation, which does not explain at all. In a vein of infiltration and in 

 very many other individual cases, corrosion may be and probably is 

 the correct explanation. But in veins of segregation, or in highly 

 metamorphic rock masses where crystals occur with rounded angles 

 and edges, neither "fusion" nor "corrosion" appear equal to the 

 task which is set for them. 



Explaining their forms, however, by saying that they are the 

 result of crowding, or growing in a pasty mass, or of a general 

 crystallization throughout the entire mass, clears away much that is 

 otherwise hard to explain and affords at least an excellent working 

 hypothesis. 



