398 University of California Publications in Geology [Vol. ll 



An objection, which might be made, is that the regular bedding 

 would not be expected on the notion of segregation. The objection is 

 robbed of its force when certain similarities between this bedding and 

 the bandings produced by diffusion reactions in colloids are considered. 



Liesegang showed that if a glass plate were coated with gelatine, 

 impregnated with potassium bichromate, and a drop of silver nitrate 

 solution were placed on the plate, that a series of concentric rings 

 of silver chromate would be formed around the drop. The rings of 

 the precipitate were closely spaced in the neighborhood of the drop of 

 silver nitrate, but became successively further and further apart as 

 the distance from the center increased. 



In some excellent figures, recently published by Stansfield, 104 it 

 may be seen that while these Liesegang rings are fairly regular, they 

 are by no means perfectly so. They show a frequent wedging out of 

 the bands and many other small irregularities. 



Morse and Pierce 105 modified the experiment somewhat, and 

 allowed solutions to diffuse down into test tubes, filled with gelatine 

 which had been impregnated with various reagents. They found that 

 as the diffusion proceeded, horizontal bands were formed in a direc- 

 tion transverse to the test tube. They formed bands of this kind, 

 consisting of other substances than silver chromate, even forming 

 strata marked out by numerous bubbles of carbon dioxide. In this 

 experiment the bands were more closely spaced near the top, from 

 whence the diffusion was proceeding. Stansfield has shown that, 

 under certain conditions, it is possible to set the bands equally spaced 

 instead of arranged at progressively increasing distances. 



Bradford 106 has called attention to the peculiarities of certain of 

 these stratifications. He experimented with test tubes containing 

 agar gel in which small amounts of either potassium sulphide or of 

 manganese sulphate had been dissolved. In any case the tube was 

 treated with a solution of the other reagent. 



The resulting stratification of the manganese sulphide is different 

 from any stratification of this sort which has hitherto been produced. 

 The difference consists in that many of the zones are separated into 

 a number of concretions, which in some cases are joined by rods 

 to those of succeeding zones. He points out that these structures 



is* Stansfield, J., Retarded Diffusion and Rhythmic Precipitation, Am. Jour. 

 ScL, vol. 43, p. 1, 1916. 



165 Morse, H. W., and Pierce, G. W., Diffusion and Supersaturation in Gelatine, 

 Proc. Am. Acad. ScL, vol. 38, p. 625, 1902-03. 



166 Bradford, S. 0., The Liesegang Phenomenon and Concretionary Structures 

 in Rocks, Nature, vol. 97, p. 80, 1916. 



