REDISTRIBUTION OF ELEMENTS IN THE FORMATION 
OF SEDIMENTARY ROCKS? 
WARREN J. MEAD 
PROBLEM 
Sedimentary rocks are derived from the destruction of older 
rocks—igneous, crystalline, and sedimentary. ‘The pre-existing sedi- 
mentary rocks may themselves have come from still earlier sediments, 
and these in turn from earlier ones, and so on back, but ultimately 
their derivation may be traced to the igneous and crystalline rocks, 
the latter term being used to include schists and gneisses resulting 
from the metamorphism of the igneous and sedimentary rocks, and . 
others whose origin cannot be determined. Obviously igneous rocks, 
and the crystalline rocks of the Archean or Basement Complex, 
whatever their origin, have yielded the materials for all later sedi- 
ments, some of which have gone through several cycles of erosion 
and redeposition. 
The development of a sedimentary rock from an igneous or crys- 
talline rock involves redistribution of the materials, both minerals 
and elements. In the process of weathering, certain materials are 
taken into solution, while others are not. Of the materials not dis- 
solved, some are removed by erosion as finely divided rock particles— 
mud, silt, and sand. The remainder consists of the partially weathered 
rock and residual clays which remain 7m situ where erosion lags 
behind such alteration. 
The material transported in a solid state, upon deposition, forms 
the mechanical sediments of shales, sandstones, etc. Of the material 
carried in solution, a portion is deposited as cementing and vein- 
filling materials during the process of transportation. After reaching 
the sea, a part of the remaining material is precipitated, forming the 
chemical and organic sediments, the limestones, and other carbonates; 
1 This is the first of a series of articles on metamorphic problems to come from 
the Metamorphic Laboratory of the University of Wisconsin. ‘The next title will be 
“The Metamorphic Cycle,” by C. K. Leith. 
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