3*i 1 A. WINCHELL — RESULTS OF ARCHEAN STUDIES. 



movements of the t \\ < > masses of rock material. But there is no evidence 

 of any other than very slow and gentle movements. It would appear that 

 the plasticity evident in the included gneissoid fragments extended, also, to 

 the schist, though in a less degree. Nothing appears to prove whether the 

 gneissoid fragments were introduced during the sedimentary deposition of 

 the pre-schistic heds — the layers of soft sediments adapting themselves to 

 the introduced masses; or were thrust into the body of schist after consoli- 

 dation and re-softening — the layers of schist adjusting themselves to the 

 foreign bodies. There are, however, no traces of lines of travel through 

 the schists, indicating that the fragments had reached their position through 

 some passage opened from the place of entrance into the schists. Their 

 environment is as uninterrupted and close as if the fragments had been 

 original enclosures. 



Phenomena of the class cited above have not been very widely recorded. 

 But they are not unknown. Dufreuoy and Elie de Beaumont have de- 

 scribed the massif of central France as composed almost entirely of granite 

 and gneiss, the " latter passing up into mica schists and downward into fine- 

 grained granite, with which it alternates."* Alternations of granites and 

 gneisses have also been described from America f and other countries. M. 

 A. Michel-Levy, in discussing the crystalline rocks, speaks of these inter- 

 beddings as somewhat familiar-! 



MlM.KALOGICAL RELATIONS OK THE GRANITOID, GNEISSOID, AND S< HIST- 

 OID Rocks. 



Throughout the Northwest it is difficult to distinguish recognized gneiss 

 from recognized schists of the mica and hornblende bearing sorts by any 

 mineralogical character except its larger percentage of feldspar.§ It is true 

 that the gneisses are generally coarser and heavier bedded, but they are not 

 always so. It is true that the schists occupy on the whole a different hori- 

 zon ; but I find them frequently in the same horizon. When I examine 

 closely the characters of the constituent minerals I find nothing about the 

 quartz, nor the micas and hornblendes, nor the feldspars by which I can say 

 that a given character belongs rather to the gneisses or to the schists. || 



I. de la France, vol. 1, 1841, p. 109; Prestwioh, G f ol. i, 1886, p. 421. 



e, for Instance, Ring, I'm tieth Pi , vol. i, 1878, p. 102. 



ttione in tin- acidic gneisses, he Bays: " Ces Intercalations sont touj "8 



parnli' ilea ;> in Bchistositd. * * * Lea gneiss acides >-\ '!<• plus en pin* oristallins dominent :i In 

 jpiii.s il>- admettenl des Intercalations frequentes de micaschistes •■( de leptynites, auquels 

 • Hi 'i.- nombreui dellts d'amphibole ••' de clpolin.' 



Bull, di '•■ gePlog. 'I'- Frai _ Nov., i> s 7. p. 103. 



facl tin- i ii Doted of other regions. King Bays: "The crystalline Bchists and gneisses 



formed of Identically tl mhydroufl minerals which characterize the granites. * * * 



me minerals, and, furthermore, theii copical Btruoture and i he 



character of their foreign inclusions are identical." King, Fortieth . ol. i, 1878, pp, 



117 i 



This is meant rather for a provisional than a final statement M, \ Michel-L6vy has enumei 

 microscopic character! by which be thinks the crystalline •-'•lii-i- differ Irom the gneia 

 106. 



