StockdoJe: Stylolites 



73 



shales which show 2.90 per cent of FeO and 4.04 per cent of 

 Fe,0, (Clarke, F.W., 1916, p. 546). Clarke points out that 



In the shales the proportion of ferrous relatively to ferric oxide has 

 increased; probably because of the reducing- action of organic matter in 

 the sediments as they were first laid down. Ferric oxide has been evi- 

 dently reduced, and organic substances furnish the most obvious reagents 

 for iDroducing such an alteration. 



That most of the parent limestone is lost in its decomposi- 

 tion is well shown in Tables Xo. 1 and 2, column III. In the 

 first, 87.75 per cent of the original rock was lost, while in 

 the second, 90.86 per cent. The amount of loss of the parent 

 rock is dependent, of course, upon the ciuantity of soluble 

 materials. The order of loss of the various constituents is 

 somewhat variable in different cases, but commonly occurs as 

 follows : 



a. Lime — removed in most appreciable quantities, usually 



90-100 per cent. 



b. ^Magnesia — usually more resistant than lime, altho in some 



instances it is dissolved more rapidly than the lime. 



c. Soda — solubility often fairly high, altho variable. 



d. Potash — solubility low as compared with lime. 



e. Iron oxide — solubility quite variable, depending upon 



whether it exists as ferrous or ferric oxide, the former 

 being more readily dissolved. ^lost of the iron of the 

 residual clay occurs as ferric oxide. 

 /. Alumina — practically insoluble. It may be removed in 

 part, however, as aluminum sulfate, if the limestone 

 contains pyrite. 



g. Silica — practically insoluble. It may also be partially 

 leached out if the rock contains alkalies in appreciable 

 quantities. 



The writer vishes to present three tables of analyses — 

 Tables Xo. 4, 5, and 6 — to show the chemical relationship 

 between the clay partings of stylolite-seams and the associ- 

 ated limestones. Each table gives the analysis of the fresh 

 limestone (column I) : the analysis of the clay of the stylolite- 

 seam (column II) ; the percentage of loss of the entire rock 

 (column III) ; the percentage of each constituent saved (col- 

 umn IV) ; and the percentage of each constituent lost (col- 

 umn V). Columns III, IV, and V were calculated on the 



