BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 1, pp. 357-394 April 15, 189o 



SOME RESULTS OF ARCHEAN STUDIES. 



BY ALEXANDER WINCHELL, A. M., LL. D., F. G. S. A., PROFESSOR OF GEOLOGY 

 AND PALAEONTOLOGY IN THE UNIVERSITY OF MICHIGAN. 



(Read before the Society December 28, 1880.) 



ANALYSIS. 



Page. 



Conflicts of Opinion in this Field 357 



The Northwest compared with New England ard Canada 359 



Areas of Granitoid and Gneissoid Rocks_ 361 



Areas of Crystalline Schists ^ 366 



Structural Relations of the Granitoid, Gneissoid, and Schistoid Rocks 367 



Mineralogical Relations of the Granitoid, Gneissoid, and Schistoid Rocks 374 



Areas of Semi-Crystalline Schists 377 



The Lithological Constitution of the System of Semi-Crystalline Schists 378 



Argillite, with the Ogishke Conglomerate 379 



Altered Tuffs and Mixed Rocks 381 



Porphyrellite 382 



Gniywacke 382 



Structural and Mineralogical Relations of the Crystalline and Semi-Crystalline 



Schists 383 



The Uncrystalline Schists 385 



Classification of the Foregoing Rocks 389 



Discussion 391 



Conflicts of Opinion in this Field. 



The present memoir is simply a synopsis of facts observed by the author, 

 with a few obvious inferences, touching the structure and classification of 

 the older rocks of the Northwest. Citations will be made from other inves- 

 tigators where the facts or opinions appear to throw important light on the 

 problems which the author has studied. 



The motive for offering this presentation of the results of personal studies 

 exists in the vague and conflicting state of opinion respecting the older rocks. 

 This concerns not only their genesis and geological history, but their con- 

 stitution and characters and even their sequence and mode of mechanical 

 relation to each other. On the one hand, there are geologists of reputation 

 who maintain that most granitic and gneissic rocks have originated directly 

 XLVII— Buj,l. <TF.or,. Soc. Am., Vol. 1, 1889. (357) 



