THE 
HWOURNAL: OF GEOLOGY 
WMAYV-/ ONE, 1007 
THE. METAMORPHIC CYCLE 
©) kK. LEICE 
University of Wisconsin 
Katamorphism.—Igneous rocks, when affected by meteoric 
agencies at and below the weathering surface, tend to become adjusted 
to their new environment in such a manner that their constituents 
become distributed as follows: 
Mechanical sediments— 
Shales 
Sandstones 
Conglomerates, etc. 
Carried as solids 
Material re- : 
moved Chemical sediments— 
Original igneous Carried in solu- Limestone, etc. 
p . Cementing materials 
and crystalline tion Vein-filli ‘al 
ange ein-hiling materials 
Mineral matter of the sea 
Material remainin { BVoameted stocks 
Der eae Residual clays and soils 
Fully 97 per cent. of the end-products are sediments. included 
under the general names of shales, sandstones, and limestones. 
Arkoses, graywackes, conglomerates, etc., containing original com- 
plex silicates, may be regarded as intermediate stages of alteration, 
and may thus be disregarded in a consideration of ultimate products. 
Of these the shales are by far the dominant sediments, as shown by 
field observation, by measurement of river loads, and _ by calculations 
of the relative proportions of the three sediments necessary most 
nearly to approximate the composition of the parent rocks. The 
last method, which is well based, puts the average percentage of 
shales, derived from the average igneous or crystalline rock, as high 
as 79 per cent., the sandstones constituting 12 per cent., and the lime- 
Vol. XV, No. 4 303 
