GEOLOGICAL EXPLORATIONS AND LITERATUKE. 73 



the underlying- graTiitc, wliieh is a poiijliyiitic l^iiiil largely composed of acryptocrys- 

 tallinc felsitic iii-omidiiiass inclosiin;- quartz j;iaiiis and ort-hoclase crystals of larger 

 size. This peculiar variety of granite is typical for the smaller intrusive belts, aud most 

 likely the granite in this caseciarae in contact with tlu^ conglomerate l»e]t l)y intrusion. 

 Better proof for the deposition of Pluronian sediments on a base of granite is furnished 

 by another locality in the SE. i of Sec. 22, T. 47, R. 20, where several knobs, centrally 

 composed of massive granite, are surrounded by a mantle of coarse granite breccia, 

 with a well laminated quartzo.se material as a cement. This breccia is conformably 

 succeeded by a series of steel gray colored shining hydro-micaceous slate rocks inter- 

 laminated with heavy belts of light colored compact quartzite. . . . 



The uplieavalof the granite and its intrusion into the overlying strata occurred 

 in all probability near the termination of the Iluronian period, as we find the granite 

 in contact with any of the Huronian strata, up to the youngest, and these always in a 

 dislocated position. . . . 



The dislocation of the Huronian beds is not exclusively due to the ui)heaval and 

 intrusion of the granite, as numerous other intrusive rock belts, dioritic or diabasic, 

 intersect the granite as well as the incumbent beds. 



Whitney (J. D.) and Wadsworth (M. E.). The Azoic System and its Proposed 

 Subdivisions. Bull. Mus. Oomp. Zool., Harvard Coll., whole series vol. Vti (Geological 

 series vol. i), 1SS4, pp. .%.'>. 



Part I of this work is a critical "Synopsis of tlie Evidence on which 

 the Rocks of the Azoic System have been variously grouped into Distinct 

 Divisions by American Geologists," and occupies most of the volume, taking 

 up in a geographical order all that has heen written to (Lite on the Arclieau 

 or Azoic geology of Canada and the several states of the United States 

 within which these ancient rocks come to the surface. Part ii, which is a 

 "Resume and General Discussion", in which the Authoi-s offer ''a brief 

 synopsis of the conclusions at which we have arrived in the study of these 

 older rocks." 



To any geologist who had concerned himself with the study of the 

 pre-Cambrian formations in the years innnediately preceding the appear- 

 ance of this volume, it must have become very evident that some sort of 

 a critical review of all that had been written with regard to these ancient 

 rocks was quite necessary to future progress in investigation. P^or -aore 

 than one reason, what had been written prior to this time had ref-.uted in 

 the greatest of confusion. In the first place the \'ery nature of the rocks 

 themselves were such as to l)afifle iintst of the attempts of the oldm- gi^ilo- 



