304 CK. ELT 
stones 9 per cent. of the total of these three sediments.* Averages 
of sections made from field observations give uniformly a lower per- 
centage of shales and higher percentage of limestone. An average 
of twenty-one sections from different parts of the United States shows 
30 per cent. of limestone. If the difference of proportion determined 
by the chemical and field methods is a real one, as inspection of the 
data used seems to indicate, the significant questions are raised, (1) 
whether there may not be a concentration of limestones on continen- 
tal areas, their complementary shales and muds being in the deep sea; 
or (2) whether limestone may not be concentrated in the upper, 
observed, part of the lithosphere, because of its known inability to 
remain in the deep-seated zones of high pressure and temperature. 
But whether the differences in results reached by the two methods 
are real or apparent, there is sufficient accordance in the main fea- 
tures of the redistribution of the elements for the purposes of the 
following discussion. 
The changes summarized in the table are destructive or katamor- 
phic (Van Hise) or descensional (Chamberlin and Salisbury). Chem- 
ically there is a sundering of complex silicates. The bases, for the 
most part, go off in solution and are precipitated as oxides, carbon- 
ates, sulphides, and even silicates, or remain in solution, a notable 
instance being sodium chloride. Kaolin develops simultaneously 
through the hydration in place of the remaining alumina silicates. 
Neither the free quartz nor other oxides are greatly changed. 
The mineralogical changes, so far as quantitatively known, may be 
roughly expressed by a comparison of the minerals of the average 
parent rock, and of the end-products in above proportion of sediments, 
as in the following diagram. 
Feldspars obviously yield much the largest part of the shales, and 
a relatively small part comes from the ferromagnesian minerals. 
Quartz becomes more abundant in the katamorphosed rocks. The 
quartz of the sandstone may be regarded as corresponding in amount 
approximately with the free quartz of the igneous rock, indicating 
that the quartz of the shales is derived largely from the pre-existing 
feldspars. The minerals of the limestone and allied sediments are 
1 W. J. Mead, “Redistribution of Elements in the Formation of Sedimentary 
Rocks,” Journal of Geology, Vol. XV, No. 3, pp. 238 ff. 
