380 The American Geologist. cane ae 
struggle off at right angles to the dike, while large masses of 
tourmaline may be separated from the dike by several feet of 
unchanged schist. Or a dike two or three inches wide may 
show no tourmaline zone, while a mere film of quartz may 
have a considerable zone on each side. In other cases, the 
tourmaline forms narrow marginal zones in the granite dike 
itself, frequently sending strings and bunches well into or 
quite across the dike. Indeed, it is quite impossible to des- 
cribe the extreme irregularity of shape, size, and distribution 
shown by the tourmaline zones. 
At some exposures, there is a network of the tiny dikes 
so that the surface of the schists is marked by a series of 
black ridges, since the tourmaline rock is resistant to weather- 
ing. 
In a general way, the amount of tourmaline seems to vary 
inversely as the width of the dikes. There is no doubt that 
the smallest dikes have tourmaline zones disproportionately 
large as compared with the zones of wider dikes. Apparently, 
too, the amount of tourmaline becomes relatively greater as 
the offshoots become more quartzose. This is, however, little 
more than a restatement of the preceding relation, since the 
narrow offshoots are usually the richest in quartz. 
The phenomena sketched resemble in many ways those 
described by Patton,* ‘though on a smaller scale; and they 
evidently have been produced by a class of processes, now gen- 
erally regarded as explaining many pegmatytes and ore de- 
posits, in which gases, vapors, and very hot solutions de- 
rived from igneous magmas are the most potent factors. 
It seems probable that the granite magma was forced, un 
changed, into the larger fissures of the schists, while, being 
charged with water vapor and gases, it was subjected to a 
process of separation, by which the vapors and very fluid pro- 
ducts of hydro-thermal fusion were injected into the narrow- 
er cracks, often wandering far from the main intrusive 
body. The larger cracks would thus be filled by the more 
normal granite magma. And as a matter of fact we find in 
them the tourmaline granite of somewhat pegmatitic habit. 
The smallest cracks, on the other hand, should show the wid- 
*H.B. PatTtTon. Tourmaline and Tourmaline schists from Belcher Iiill, 
Colorado. Bull. Geol. Am. X, pp. 21-26. 
