GEOLOGY: S. TABER 
663 
can expel solutions occupying subcapillary pores in rocks; and in ser- 
pentine and other rocks found enclosing cross-fiber veins the openings 
are almost entirely subcapillary in size. In such cases the transfer of 
material to the growing vein is probably due to diffusion rather than 
to circulation. 
A central parting is formed whenever fibers start to grow from both 
walls of a fracture, and apparently this always happens when veins 
develop along pre-existing fractures unless growth is limited to one side 
only. In laboratory experiments, growth is frequently limited to one 
side by the development of the fracture in such a direction as to cut 
the other side off from solutions furnishing material for growth. When 
the formation of the fracture and the beginning of vein growth are con- 
temporaneous, the parting is absent because of simultaneous growth 
at both ends of the fibers — a fact proved in the laboratory by chang- 
ing the color of the solutions so as to produce symmetrically banded 
veins. Partings may also result from a pause in the process of growth 
or from a slight displacement of the walls. The irregularity of some 
partings is due to the more rapid growth of groups of fibers most favor- 
ably situated to receive additions of new material. 
The inclusions of wall rock found along central partings represent 
fragments formed when rupture occurred, and their position is due to 
the growth of the vein on both sides as new material was added through 
the walls. Occasionally vein matter begins to crystallize along an in- 
cipient fracture or line of weakness close to the vein, and in this way 
a fragment is gradually separated from the wall and included in the 
growing vein. 
The fibers are always parallel to one another and extend in the di- 
rection in which the walls moved as they were pushed apart by vein 
growth. In most veins the fibers are normal to the walls because the 
latter have been forced directly apart, but when the walls have had 
also a lateral displacement because of the simultaneous growth of ad- 
jacent non-parallel veins or other causes, the fibers grow in the direction 
of the resultant motion. If the course of the vein is not straight, the 
fibers may be normal to the walls at one place and oblique at another. 
As long as the relative motion of the walls of a growing vein is in a 
straight line, the fibers are straight; any change in the direction of 
motion is immediately recorded by the slowly lengthening fibers. 
If the change in the direction of relative motion is gradual and contin- 
uous the fibers are curved; if abrupt, it results in the development of 
sharp bends. Sometimes the fibers of a chrysotile vein record several 
changes in the relative movement of the walls, and this gives a banded 
