METAMORPHIC STUDIES 261 
The discernment of these results will require a much wider range 
of study and quantitative observation than we have before 
attempted. 
The acceptance of this view of the significance of the meta- 
morphic cycle involves perhaps a slight modification of the prevalent 
interpretation of Hutton’s great law of uniformitarianism, that the 
present is the key to the past. In metamorphism the same series 
of processes are operating today that have operated in the past, 
but they have slowly made over the rock types and redistributed 
them vertically and horizontally, with the result that while the 
same processes act today as have acted in the past, they are today 
operating, we infer, on different proportions and distributions of 
substances, with consequently differing emphasis and producing 
slightly different results. 
