R^SUMI^, AND GENEKAL DISCUSSION. 



561 



coarsely crj-stallinc diabases and diorites were erected into the Norian ; 

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

 finer-grained diorites, diabases, melapliyrs, and chlorite schists were 

 formed h»to 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 fragmcntal forms of each rock were placed 

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

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

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

 believe in the lithological subdivision of the crystalline rocks into 

 geological formations, we would propose another arrangement, wliich 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- 

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

 new series ; do the same for the peridotitcs, 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 

 satisftxctory evidence as that on which the formations now accepted are 

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

 quette iron ores are unconformable with the Huronian ; the segregated 

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

 resulting serpentines, with theirs, etc. 



Present Chronological 

 .'tic > 



} 

 } 



Coarse-grained Trachytic 

 Rhyolitic Rock 



Coarse-grained Basaltic 

 Rock. 



Compact Rhyolitic and 

 Jaspilitic Rocks. 



Fine-grained Basaltic 

 Rocks. 



Trachytic and IMetamor- 

 pliic Rocks. 



Metamorphic Rocks. 



VOL. VII. — NO. 11. 



Arrangement of the Crystalline Rocks. 



J (Coa 



\ Gr 



XORIAN. 



Arvoman. 



Huronian. 



Montalban'. 



Taconian. 

 SO 



Coarse-grained compact 

 anites and Gueis.-^es. 



( Gabbro, and some Diabases 

 \ and Diorites. 



f Felsite. Petro.silex. Quartz 

 \ Porphyry, Jaspilite. 



5 Diorite. Diabase. Melaphyr, 

 ( Chlorite Schist. 



f Friable Granites, Mica 



( Schists. 



j Quartzites, Limestones 

 I and Argillites. 



