xiiSsum:^, and general discussion. 



561 



coarsely crystalline diabases auddiorites were erected into the Norian ; 

 the fclsitcs and quartz porphyries were placed as the Arvonian ; the 

 finer-grained dioritcs, diabases, melaphyrs, and chlorite schists were 

 formed into the Huronian ; the more friable granitic and gncissic rocks 

 with the mica schists were classed as Montalban ; and the quartzites, 

 limestones, and argillites were united into the Taconian. Of course in 

 each case the metamorphic fragmental forms of each rock were placed 

 with the rocks they resembled, while the other forms of crystalline rocks 

 were distributed through the groups. Wo give below these arrange- 

 ments in a tabular form j and in order to aid those geologists who 

 believe in the lithological subdivision of the crystalline rocks into 

 geological formations, we wpuld propose another arrangement, which will 

 be still more in harmony with their views. Thus we would place all 

 the granites, gneisses, and syenites in the Laurentian ; erect the mag- 

 jictites, menaccanites, hematites, and their associated jaspilite into a 

 new series 3 do the same for the peridotites, including the serpentines ; 

 but leave the Norian, Arvonian, and Huronian as they now stand. Fur- 

 ther, we may place the porphyrites in a new group; limit the name 

 Montalban to the mica schists, and the Taconian to the limestones; 

 and place the quartzites, conglomerates, and argillites in three additional 

 and distinct groups. All these divisions can be supported by quite as 

 satisfactory evidence as that on which the formations* now accepted are 

 sustained. For instance, there is indubitable evidence that the Mar- 

 quette iron ores are unconformable with the Huronian ; the segregated 

 limestones with their associated rocks; the eruptive peridotites, and the 

 resulting serpentines, with theirs, etc. 



5 ^ 



Present Chronological Arrangement of the Crystalline Rochs, 



Coarse-grained Trachytic 

 Khyolitic Rock. 



Coarse-grained Basaltic 



Kock. 



Compact Khyolitic and 

 Jaspilitic Kocka. 



Fine-grained Basaltic 



Uocks. 



Trachytic and Metamor- 

 phic Kocks. 



Metamorphic Tlocks. 



VOL. VII.— NO. 11. 



Laurentian 



NOKIAN. 



Arvonian, 



HuRONIAJf. 



MoNTALnAN. 



Taconian. 



30 



( Coarse-grained compact 

 I Granites and Gneisses. 



5 Gabbro, and some Diabases 

 ( and Diorites. 



lelsite, Petrosilex, Quartz 

 Porphyiy, Jjispilite. 



5 Diorite, Diabase, Melaphyr 

 I Chlorite Schist. 



Friable Granites, Mica 



Sch ists. 



5 Quartzites, Limesioncs 

 ( and Argillites. 



:i<<i 



J 



} 



L',5 



