EVOLUTION OF LIMESTONE AND DOLOMITE 401 



chemical compositions, in which he distributes the average igneous 

 rocks into shales, sandstones, and limestones in the ratio of 80: 15 : 5. 



An earlier estimate by Van Hise 1 divides the sedimentary rocks 

 into 65 per cent shales, 30 per cent sandstones, and 5 per cent 

 limestones. 



A computation made by myself, using Mead's method, shows 

 that a composite Georgia 2 granite made from Watson's analyses 

 is nearly equivalent to a mixture of composite Georgia clay (Wat- 

 son's) and average sandstone (Clarke's) in the ratio of 55:45, not 

 enough lime and magnesia being present to be available for lime- 

 stone. Another computation by myself shows that a composite 

 basic rock made up from composites of diabase, gabbro, basalt, 

 and peridotite in the ratio of 6:6; 6:1 is equivalent to average 

 shale and limestone (Clarke's) in the ratio of 88:12. The upshot 

 of ail these computations and estimates seems to be that the 

 predominant igneous rock types are equivalent to a large per- 

 centage of elastics, predominantly mud or shale, and a relatively 

 small percentage of limestone, hence the same would be true of 

 the primitive lithosphere, regardless of whether it was entirely 

 rhyolite or entirely basalt. 



Under the theory of the stability of oceanic and continental 

 segments, the redistribution of the primitive lithosphere into 

 sediments may have taken place along one or the other of two 

 uniformitarian directions. The redistribution materials may 

 have been deposited upon the continents and in the oceans in 

 such proportions as to leave the composition of the lands unchanged. 

 This might be termed "integral" redistribution, because it leaves 

 the composition of the lands as a whole as it was before. Obviously 

 " integral" redistribution of the redistribution materials to the 

 nth power would not change the composition of the lands. But 

 redistribution has certainly changed the composition of the lands 

 with respect to one element at least — sodium. That the lands 

 contain less sodium now than in the past, in consequence of leach- 

 ing and the accumulation of non-sodiferous sediments on the 



1 C. R. Van Hise, "Treatise on Metamorphism," Mon. U.S.G.S., XLVII (1904), 

 94o. 



2 Watson, Bull. No. g-A, Geol. Survey of Georgia. 



