450 F. H. Lahee — Metamorphism and Geological Structure. 



General and theoretical considerations. — As in the discus- 

 sion of the structural geology of the Basin (Part I of this 

 paper), here also we shall put theory before fact. Accepting 

 the doctrine commonly held to-day, namely, that most peg- 

 matites are of magmatic derivation,* we shall review below 

 certain facts which may assist in the determination of the 

 relations between the Acid Intrusive Series and the Basin 

 sediments. 



The importance of the role played by catalyzers, or mineral- 

 izers, in the crystallization of magmas, and especially of acid 

 magmas, is w T idely recognized. These mineralizers "have been 

 defined as volatile substances which, without entering into the 

 final composition of minerals, render possible or facilitate their 

 formation and crystallization. "+ This they do by reducing the 

 viscosity of the magma and by lowering the freezing-points 



of its constituents.^: Harker continues, "There is no 



reason for excluding the case in which the mineralizer, or part 

 of it, enters into the mineral as finally constituted."! Among 

 the chief catalytic agents may be cited fluorine, chlorine, boric 

 acid, carbon dioxide, hydrogen, and water gas.] 



* For summaries of theories for the origin of pegmatite, see the following : 



Brogger, W. C, Die Mineralien der Syenitpegmatitgange der siidnor- 

 wegischen Augit und Nephelinsyenite. Zeitschr. fur Kryst., xvi, I Theil, 

 pp. 215-225, 1890. Trans, by N. N. Evans, Can. Eecord of Sci., vi, np. 33- 

 46 and 61-71. 



Williams, G. H., General Eelations of the Granite Rocks in the Middle 

 Atlantic Piedmont Plateau, U. S. G. S., Ann. Kept., xv, p. 657, 1894. 



Van Hise, C. R., A Treatise on Metamorphism, U. S. G. S., Monog. xlvii, 

 1904. Pp. 721-724. 



For recent statements on the subject, see : 



Harker, A., Natural History of Igneous Rocks, N. Y., 1909. 



Iddings, J. P., Igneous Rocks, N. Y., 1909. 



Bastin, E. S., Geology of the Pegmatites and Associated Rocks of Maine. 

 U. S. G. S., Bull. 445, 1911. 



\ Harker, A., op. cit., p. 286. 



\ Daubree early demonstrated the function of water in promoting the 

 crystallization of anhydrous minerals far below their fusion points. 

 (Daubree, A., Etudes synthetiques de Geologie Experimental e, Paris, 1879, 

 p. 234.) 



§ Harker, A., op. cit., p. 287. Thus, muscovite, containing OH, maybe 

 regarded by the aid of mineralizers. Nernst, however, defines the process of 

 catalysis as "an increase in velocity of reaction caused by the presence of 

 substances which do not take part in it, although the reaction is capable of 

 taking place without their presence." (Nernst, W., Theoretical Chemistry. 

 London, 1904, p. 566.) See also Doelter, C, Physikalisch-Chemische 

 Mineralogie, Leipzig, 1905, pp. 115 et seq. 



Writing on this subject, Bastin suggested the application of Raoult's law 

 to rock magmas ''to the extent that magmatic constituents of low molecular 

 weight may exert greater influence in lowering the freezing point, decreas- 

 ing the viscosity, and affecting textures, than do constituents of high mole- 

 cular weight" (Bastin, E. S., op. cit., p. 31). 



I See Harker, A., op. cit., p. 295. Among the catalyzers, especial 

 importance is attributed, by Bastin (op. cit., pp. 30-31), to the influence of 

 water gas and of hydrogen in helping the crystallization of pegmatite. 

 These substances largely escape as the magma cools. 



