PRINCIPLES UNDERLYING METAMORPHIC PROCESSES 621 
The same observation has also been made by others, among 
them L. Hezner’ in schists of the Gotthard region. In this case the 
additions did not take place at the period of intrusion, but during 
the tectonic disturbances, a fact which shows that the phenomenon 
is not due to a difference of volatility of soda and potash compounds 
at high temperatures, but to differences of solubility. Correspond- 
ing to this, the solutions emanating from eruptive rocks usually 
contain more soda than potash, a fact which is correlated with 
the high soda content of sea-water. 
The occurrence of relatively small amounts of such substances 
as hydrofluoric acid, boric acid, hydrofluosilicic acid, which often 
are present in magmatic solutions and emanations, can be noted in 
the mineral content, though the general characteristics of the rock 
are otherwise altered but little. Such additions produce certain 
minerals characteristic of contact-metamorphic rocks: such as 
fluorite (F), scapolites (chlorides), axinite, tourmaline (B), ores 
(S, As, Sb), lime silicates or quartz in metamorphosed carbonates 
(Si). 
If intrusion proceeds relatively rapidly, or if solutions (fluid or 
liquid) at high pressure remain over from the process of solidifica- 
tion, there will be an intensive penetration of the surrounding rock 
with magmatic material. The escape of the magmatic solution 
follows along the lines of least resistance, producing numerous veins 
and dykes; in originally sedimentary rocks the direction of these 
is that of the stratification, or in case the rock has been (or is 
simultaneously) subject to tectonic disturbance, they lie in the 
direction of the cleavage planes produced thereby. An interfolia- 
tion of the rock may therefore be produced in this way. 
A further consequence of intense penetration with hot magmatic 
material is a considerable rise of temperature in the surrounding 
rock, which produces the characteristic phenomena of thermometa- 
morphism and Sammelkristallisation (increase in size of the crys- 
tals). In the neighborhood of injected veins the crystals of a 
mineral are commonly larger than they are at some distance from 
it. The tendency to growth of crystals exists because small 
crystals of any substance are unstable with respect to larger crystals. 
t Neues Jahrbuch f. Min., Beilage Band XXVIII (1908). 
