VEINLETS IN THE SILURIAN AND DEVONIAN qi 
this force enables a crystal to grow in directions in which growth 
is opposed by external force “‘notwithstanding unrestricted oppor- 
tunity for growth in other directions; (2) that the linear force thus 
exerted is of the order of magnitude of the breaking strength of the 
crystal.”* Most of the phenomena that have been cited in support 
of the latter hypothesis may be explained, however, by the fact that 
the growing crystals have been in contact with a supersaturated 
solution in only one direction, or that the concentration of the 
solution has been greater in one direction than in others. The pres- 
ent writer believes that the pressure effects accompanying crystal 
growth are to be attributed chiefly to the molecular forces associated 
with the separation of solids from solution, and that the tendency 
to develop crystal faces is of minor importance.?, Argument in 
support of this hypothesis has been given elsewhere. 
According to the writer’s concept, the pressure developed during 
crystal growth is due, in most cases, to the fact that the solid can 
diffuse through a solution occupying small capillary or subcapillary 
spaces, while the crystalline mass built up by the separation of the 
solid from solution cannot escape through the small openings in 
like manner, even when under great pressure. The force observed 
during the separation of crystals from solution is believed to be 
analogous to the pressure developed when an anhydrous salt, con- 
fined in a limited space, combines with water that has diffused as 
vapor through capillary openings.* The diffusion of the solid 
through the solution is ascribed to osmotic pressure, and its separa- 
tion therefrom to the relation between osmotic pressure and solu- 
tion pressure. . 
Crystals grow through the addition of layers of material to their 
outer surfaces, and this can take place only when the surfaces are in 
contact with a layer of supersaturated solution, the concentration 
1G. F. Becker and A. L. Day, ‘‘ Note on the Linear Force of Growing Crystals,” 
Jour. Geol., XXIV (1916), 313." 
2 Stephen Taber, ‘“‘The Growth of Crystals under External Pressure,” Am. Jour. 
Sci., Series 4, XLI (1916), 553-54. 
3 Stephen Taber, ‘‘ Pressure Phenomena Accompanying the Growth of Crystals,” 
Proc. Nat. Acad. Sci., III (1917), 297-302. 
4Stephen Taber,.‘‘The Genesis of Asbestos and Asbestiform Minerals,” Bull. 
Am. Inst. Min. Eng. No. 119, 1916, pp. 1986-87. 
