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Lake dej1osits include silt, sand, and, locally, peat. Dn rl~-greenish-gray vorphyriti.c andesite sills, probably of Oligocene age, intruded the sedimentary rocks in many places. A greenish-gray vrophyritic hornblende andesite or dacite in Issaquah Canyon may be a volcanic vent related to the rocks of the Tukwila Formation.Known resources of coal are estimated to be about 600 million tons, of which 78 vereent is bituminous and 22 percent is subbituminohs. Potential .coal resources are much greater and are estimated to be about 5 billion tons. The Renton Formation and the UlJlWr llart of the undifferentiated Puget Group contain the princi})al clay resources of the area. Deposits of outwash gravel in the Vashon Drift are important sources for sand and gravel. Construction stone, quicksilver deposits, silica-sand deposits, and petroleum prospects are of minor economic importance in the area.

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Diagenesis and metamorphism______________________________________ 18 Geologic setting _______________________________________________________________________ _ Chemical composition of sandstones_____________________________________ 20 Distribution and paleogeography _________________________________ _ Statistical methods___________________________________________________________ 20 Stratigraphic relations __________________________________________________ _ Means_________________________________________________________________________________ 20 Sampling plan __________________________________________________________________________ _ Geochemical relations______________________________________________________ 25 Methods of analysis ________________________________________________________________ _ 12 Analysis of variance________________________________________________ 25 Direct-reader spectrometric analyses, by Raymond