374 DONALD C. BARTON 
The principles of diffusion as given by Liebesang and Cole in 
connection with the origin of flint partially explain some of the 
features of the chert of the St. Louis area. These principles seem- 
ingly explain the formation of the chert after, but not long after, 
the formation of the limestone—the position of the chert parallel 
to the stratification but independent of it, the rhythmic deposition 
of the chert, and the excessive development of the chert within a 
few hundred feet of a great uncomformity. They are equally 
applicable whether the silica is derived from organic or inorganic 
sources, and would seem to necessitate a rather general distribution 
at the start of siliceous material through the mass. The particular 
localization at a given horizon of a chert bed might be affected, 
however, through the influence of a local excess of siliceous material 
on the concentration at that horizon. The localization might also 
be affected by the solubility of the limestone of the various 
horizons. <A serious difficulty that would seem to arise in connec- 
tion with the application of these principles in the present case is 
the presence of the numerous argillaceous beds. It is difficult to 
see how much diffusion could take place through these shale beds, 
and the diffusion would seem necessarily to be confined chiefly to 
lateral diffusion through the more porous beds. 
