in the drying of a Fluid with Particles in Suspension. 223 



have tried to record may help to throw light on certain structures 

 and processes in rocks. Applying the principles we have noticed 

 here, we might anticipate (even where crystallising materials are 

 present) 



Istly. That mutual interactions may give rise to wriggling or 

 mazy forms. 



2ndly. That greater freedom of molecular motion might cause 

 more rectilinear forms. 



Srdly. That the relative ease of transmission in different sub- 

 stances or conditions of a substance may govern the forms developed, 

 as the difference between the coarser and finer sediment. 



4thly. That the form of the external boundary influences the 

 structures developed, so that streaks normal to a rectilinear figure, 

 or radial within a sphere, are caused. 



5thly. That much depends on the relative permeability of the 

 surrounding magma ; and the solidification in a molten mass, first 

 of an external crust, would act similarly to a more impenetrable 

 environment. 



PART II. 



To have fully discussed experiments in which any effect of crystal- 

 lising forces is shown would have unduly lengthened this paper, 

 and on that subject some material has been published.* My main 

 object is to call attention to the results of mere mechanical rearrange- 

 ment, on which I think no distinct notice is available. But I may 

 briefly refer to a few results of crystallisation. I experimented 

 with solutions of various salts, mixed with gelatin, with " muds " 

 of vermilion, &c., and in other combinations. 



When solutions of calcium sulphate and of gelatin were mixed 

 in varying proportions, if the solution was weak, crystallisation 

 generally seemed to start at many scattered points. At these there 

 formed small crystals or ovoid grains (like potato starch-grains, of ten 

 compound) or clusters, frequently spherulitic. In the intervals was 

 a gelatinous-looking deposit, which had no effect on polarised light. 



* H. Vater, in ' Zeits. fiir Kryst. und Min.,' 1892-6, vol. 21, p. 433 ; vol. 22, 

 p. 209 ; vol. 24, p. 366 ; vol. 27, p. 477. O. Lehmann, in Zeits. fur Kryst. und 

 Min.,' 1877, vol. 1, p. 453. ' Q.uart. Journ. Micr. Sc.,' 1855, vol. 3, p. 179, 

 PI. 13, 14 ; and 1856, vol. 4, p. 203, PI. 12, by J. GUaisher; vol. 4, p. 201, by J. 

 Spencer ; 1861, vol. 1, n.s., p. 23, by Q-. Kainey ; 1862, vol. 2, p. 128, by T. Davies ; 



1866, vol. 6, p. 137, by K. Thomas ; 1872, vol. 12, p. 118, by Professor Harting. 

 1 Roy. Soo. Proc.,' 3866, vol. 15, p. 314, by E. Montgomery. ' Trans. Brit. Assoc., 



1867, p. 127, by Dr. Heaton. ' Phil. Mag., 1878, vol. 6, p. 113, by F. Guthrie. 

 ' Intellectual Observer, 1865, vol. 6, by H. N. Draper. ' Trans. Eoy. Micr. Soc.,' 

 1871, p. 50, by H. S. Slack. ' On the Influence of Colloids upon Crystalline Form, 

 &c.,' by Dr. W. M. Ord, 1879. ' Nature,' 1892, vol. 47, p. 162, by Dr. J. H. 

 Gladstone. 



