REGENERATION OF MINERAL PARTICLES. 705 



porphyritic constituents in the schists and gneisses adjacent to the great 

 granite batholiths of western Massachusetts." 



Occasionally there may be present in schistose rocks porphyrinic min- 

 erals which show a marked tendency toward similar crystallographie or 

 dimensional orientation, or both. 



To instances of orientation of porphyrinic constituents the arguments 

 above given in reference to the usual development of porphyritic minerals- 

 under mass-static conditions after movement has ceased are not applicable. 

 This case is discussed on pag-es 687-688. 



REGENERATION OF MINERAL PARTICLES. 



The regeneration 6 or rejuvenation in the zone of anamorphism of large 

 mineral particles which have been partly altered in the belt of weathering 

 or the belt of cementation is closely analogous to the growth of porphyritic 

 minerals. Such partly destroyed large minerals are sometimes regenerated 

 at the expense of the small ones for the same reason that the porphyritic 

 minerals form. As an illustration of the process, the feldspars may be 

 cited. In the belt of weathering they are likelv to become cloudy in 

 consequence of kaolinization, development of chlorite, zeolite, deposition 

 of iron oxide, etc. In the belt of cementation they may become cloudy, 

 in consequence of zeolitization or other alterations. When such altered 

 feldspars pass into the lower zone the reactions may be reversed; new 

 feldspar is produced, which is controlled in its orientation by the residual 

 unaltered feldspar; the alteration products are absorbed by this new 

 feldspar or else dissolved; thus the cloudy appearance disappears, and 

 the feldspar once more becomes clear and fresh- — i. e., is regenerated or 

 rejuvenated. 



This process of regeneration is especially likely to occur where the 

 rocks pass from the zone of katamorphism into the zone of anamorphism 



a Emerson, B. K., Porphyritic and gneissoid granites in Massachusetts: Bull. Geol. Soc. America, 

 vol. 1, 1890, pp. 559-561. 



6 Wolff, J. E., Metamorphism of clastic feldspar in conglomerate-schist: Bull. Mus. Com. Zool. 

 Harvard College, whole ser., vol. 16, 1891, pp. 173-183. Weidman, S., A contribution to the geology 

 of the pre-Cambrian igneous rocks of the Fox River Valley, Wisconsin: Bull. Wisconsin Geol. and 

 Nat. Hist. Surv., No. Ill, 1898, pp. 20-24. Whittle, C. L., Some dynamic and metasomatic phenom- 

 ena in a metamorphic conglomerate in the Green Mountains: Bull. Geol. Soc. America, vol. 4, 1893, 

 pp. 155-164. Hobbs, W. H., Phases in the metamorphism of the schists of southern Berkshire: Bull. 

 Geol. Soc. America, vol. 4, 1893, pp. 167-178. 



MON xlvii — 04 45 



