5G2 



THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



Proposed Chronological Arrangement of the Crystalline Rocks. 



Laurentian 



SlDEUIAX 

 Ol'IIIAN . . 

 NOHIAN . . 



Akvonian . 

 porphyrian 

 huroxiax . 

 moxtalban 

 cuystallian 

 Taconian . 

 Glacian . . 

 Pelodian . 



Granites, Gneisses, and Syenites. 

 Magnetite, Hematite, Meiiaccanite. 

 Peridotites, including Serpentines. 

 Gabbros, coarse Diabases and Diorites. 

 Felsite, Quartz Porpiiyry, Petrosilex, Jaspilite. 

 Porpliyrites. 



Diorites, Diabases, Melapliyrs, Chlorite Schists. 

 Mica Schists. 



Quartzites, Quartz Schists- 

 Limestones. 

 Conglomerates. 

 Argillites. 



It would seem that enough has been given to show that the basis of 

 tlie subdivisious of the Azoic rocks in Canada was a purely theoretical 

 one, and that Logan's methods and opinions wei'e such, when lie com- 

 menced the survey, that no different result coiUd have been anticipated. 

 It was just as if a geologist should apply the principles used in study- 

 ing the undisturbed strata of the Mississippi Valle}'^, or the Grand Cafion, 

 to the elucidation of the structure of Mt. ^tna, and attempt to divide 

 its flows and dikes into distinct geological formations. One may take 

 the utmost care in all his measurements, may count every step from 

 Gasj)e to Georgia, and make most beautiful maps and sections ; yet, if 

 he is unable to determine the characters of the rocks he is mapping, his 

 work is worse than woi-thless, for every obscure dike that is met with 

 and every segregated mass of limestone causes a new fold and contor- 

 tion to be inserted. From the fact that the surface distribution only 

 was sought in the Grenville series — in which the limestones are prob- 

 ably of chemical origin — it would appear to us that no reliance is to 

 be placed on Logan's much vaunted work and sections here, beyond the 

 question of surface distribution ; and such seems to be the case with all 

 his and his assistants' work on the crystalline rocks. 



The present director of the Canada Survey appears to be sincerely 

 endeavoring to base his work on better methods than those current 

 under Logan's administration. All who are interested in the solution 

 of the difficult problems of Appalachian geology will sympathize with 

 him in these efforts ; for, as has been already suggested, that which is 

 done in Canada will, if well done, be of great assistance to those working 

 on the south side of the Dominion line. 



