THE METAMORPHIC CYCLE 313 
ore-bearing veins in igneous rocks. The quantitative classification of 
igneous contact effects in terms of katamorphism and anamorphism 
has not yet been accomplished, or for that matter more than begun 
on any systematic scale. It is likely to yield interesting results. But 
whatever the specific relations of the influences of igneous rocks with 
conditions determined by depth they should require little essential 
revision of our conception of the metamorphic cycle for the reason 
that the cycle is based on a comparison of net results, and not on a 
comparison or weighting of the specific causes which have contrib- 
uted to these results. 
Classification of rocks—The term ‘‘metamorphism” has in the 
past been largely applied to the development of slates, schists, and 
gneisses. This use of the term is implied in the prevalent textbook 
classification of rocks into igneous, sedimentary, and metamorphic 
divisions. The student comes to realize only with difficulty the fact 
that sedimentary rocks result from alteration of igneous rocks, just 
as do the so-called metamorphic rocks. Van Hise and others have 
included all rock alterations under metamorphism, and the same 
practice is observable in the descriptions of rock alterations by certain 
petrographers when they include under metamorphism many mineral 
changes which ultimately develop the sedimentary minerals. ‘The 
development of the cycle idea further emphasizes the necessity of the 
broad use of the term ‘“‘metamorphism,” and the desirability of 
Van Hise’s terms, ‘“‘anamorphism” and “‘rock-flowage,” to cover the 
schist-making changes formerly alone considered under metamor- 
phism. With terms thus defined, the primary genetic classification 
of rocks becomes a dual one, igneous and metamorphic, the latter 
class being dually subdivided into the contrasting sedimentary and 
schist-slate-gneiss groups. 
