SUMMARY AND CONCLUSIONS. 177 



show that a general movement occurred in the rock subsequent to the 

 formation of the ottrelite, tending to bring the ottrelite crystals parallel to 

 the schistosity. Professor Gosselet ascribes the development of the ottre- 

 lite to heat, of which the cause is unknown* The spaces left behind the 

 mineral by its movement become filled either at the time or subsequently 

 by muscovite, quartz and oxide of iron, giving rise to peculiar tufts going- 

 out from the mineral. Besides the crystals of ottrelite, M. Gosselet de- 

 scribes with great care in the same rocks somewhat irregular rounded 

 areas (noyaux) of cloudy, in part doubly refracting, material, surrounded 

 by one or more zones, differing in some respects from the core, which he 

 believes to be the remains of more elementary forms of ottrelite rather 

 than crystals — globulites. 



Summary and Conclusions. 



From the foregoing, it may be asserted with much probability that the 

 minerals of a porphyritic nature which occur in the schists, viz., feldspar, 

 garnet, staurolite, tourmaline, biotite and ottrelite, were developed in 

 originally clastic rocks as a result of the orographic disturbances to which 

 they have been subjected. Internal mechanical movement seems to have 

 played only a subordinate role in their formation, as shearing brings 

 about a crushing and tearing of the constituents not generally observable 

 in the sections. The development of the porphyritic constituents seems 

 therefore to be due to a partial recrystallization of the rock as a result of 

 what I would call static metamorphism — i. e., metamorphism in which 

 pressure is the important factor, in contrast to internal movement, though 

 heat and a mineralizer were important adjuncts. The universal dis- 

 tribution of the porphyritic feldspars might indicate that they require 

 a less intense metamorphism for their development than do garnet and 

 staurolite, and this is probably true, though it cannot be asserted that 

 some of these feldspars are not detrital grains like a portion of those de- 

 scribed by Wolff.f Evidence has been given to show that the garnet 

 developed largely before the staurolite, and that the latter probably re- 

 quires for its formation more intense metamorphic action. The stauro- 

 lite crystals have been developed, at some expense to the garnet, for iron, 

 and probably also alumina and silica. This is shown by the crown of 

 staurolite crystals about garnet in the June mountain schist. This fact, 

 taken in connection with the secondary enlargements of feldspar, garnet, 

 and tourmaline, and the probability of enlargements in the case of stauro- 

 lite, indicates that the metamorphism which these schists have suffered 



*" La formation de Pottrelite est du a une production de chaleur dont il faudra chercher la 

 cause." Loc. cit., p. 203. 

 fBulI. Mus. Comp. Zool., vol. xvi, 1891, p. 17.">. 



