The thin film of dark substance composing a stylolitic seam has generally been taken to be an inert residue of insoluble "carbonaceous and argillaceous" material. Recently it has been suggested by other authors that the clay component of such a seam promotes the solution of silica, Present observations of some Cretaceous sandstones in Alberta indicate that solution of silica is promoted by the presence of C and Fe compounds. The suggested mechanism is the reduction of the Fe to produce iron sulfide and/or iron carbonate with the release of OH (super -) ions locally increasing the pH of the intrastratal solutions.

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