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Indiana University Studies 



It has been shown that, in the transformation of lime- 

 stone to residual clay, silica and alumina are two constituents 

 which are retained with little or no loss. Therefore, one 

 finds that practically the same ratio exists between the silica 

 and alumina of a parent limestone and the silica and alumina 

 of the derived clay (see Tables No. 1, 2, and 3; columns I 

 and II). In the above analyses of limestones and stylolite- 

 clays several relationships are striking and convincing. In 

 Table No. 4 the fresh limestone contains 0.84 per cent silica 

 and 0.18 per cent alumina — a ratio of about 4.6 to 1. In the 

 clay there is 29.64 per cent silica and 7.16 per cent alumina — 

 a ratio of 4.1 to 1. The limestone of Table No. 5 contains 

 0.89 per cent silica and 0.20 per cent alumina, the ratio being 

 4.45 to 1 ; the associated clay has 39.92 per cent silica and 8.76 

 per cent alumina, the proportion being about 4.5 to 1. In 

 the limestone of Table No. 6 there is 9.58 per cent silica to 

 3.39 per cent alumina, while in the clay the amounts are 

 33.68 per cent and 10.78 per cent. In both analyses (lime- 

 stone and associated clay) silica and alumina occur in ap- 

 proximately the same ratio, 3 to 1. Thus it is seen, in the 

 three above sets of analyses, that, as far as the ratio between 

 silica and alumina is concerned, the clays of the stylolite- 

 seams fulfil the requirements of a residual limestone clay. 



A study of the relationship of the iron oxide content of 

 the fresh limestone to that of the stylolite-clay also reveals 

 evidence that the clay is of residual origin. In the limestones 

 (Tables No. 4 and 5 ; column I) , one finds the iron oxide exist- 

 ing principally as ferrous oxide, with but a bare trace of 

 ferric oxide; while in the clays (column II), the reverse is 

 noted. An oxidation of ferrous to ferric oxide is normal in 

 the decomposition of limestone to residual clay (see p. 72). 

 If the clays of the stylolite-seams were of sedimentary origin 

 — as exponents of the pressure theory would have them — one 

 would expect to find a considerable portion of their iron as 

 ferrous oxide. As the analyses show, however, the ferrous 

 oxide is low compared to the ferric. It is seen also that in 

 Table No. 4 there is a greater loss of iron oxide (column V) 

 than in Table No. 5. Such is to be expected in view of the 

 fact that in the limestone of the former the percentage of 

 ferrous oxide is greater than in that of the latter. Where 

 the iron is mainly ferrous, one may expect considerable pro- 

 portions to be dissolved (see p. 72) . Thus, from the analyses. 



