562 



THE AZOIC SYSTEM AND ITS SUBDIVISIONS, 



Froposed Chronological Arrangement of the CrysialUne Eocks. 



Laurentian .... Granites, Gneisses, and Syenites. 



SiDERiAK Maguelite, Hematite, Menaccanite. 



Opiiian Peridotites, including Serpentines. 



NoRiAK ....... Gabbros, coarse Diabases and Diorites. 



Arvonian Felsite, Quartz Porphyry, Petrosilex, Jaspilite 



PoRi^HYRiAN .... Porpliyrites. 



HuRONiAN Diorites, Diabases, Melaphyrs, Chlontc Schists. 



MoNTALBAN .... Mica Schists. 



CiiYSTALLiAN .... Quartzites, Quartz Schists. 



Taconian Limestones. 



Glacian Conglomerates. 



Pelodian Argillites. 



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

 the subdivisions of the Azoic rocks in Canada was a purely theoretical 

 one, and that Logan's methods and opinions were such, when he com- 

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

 It was just as if a geologist should apply tho principles used in study^ 

 ing the undisturbed strata of the Mississippi Valley, or the Grand Ca.fion, 

 to the elucidation of the structure of Mt. .Etna, and attempt to divide 

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

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

 Gaspe to Georgia, and make most beautiful maps and sections ; yet, if 

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

 work is worse than worthless, 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 Grenvillc scries — 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 ^rith all 

 his and his assistants' work on tho 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, aa 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 Dommion lino. 



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