84 Mr, T, Sterry Hunt 



To this notion of tbe existence of two groups of crystalline rocks 

 similar in lithological character but different in age, we have to 

 object that the hypozoic gneiss is identical with tbe Green Moun- 

 tain gneiss, not only in lithological character, but in the presence 

 of certain rare metals, such as chrome, titanium, and nickel which 

 characterise its magne^ian rocks ; all of these we have shown to 

 be present in the unaltered sediments of the Quebec group, with 

 which Sir William Logan has identified the gneiss formation in 

 question. Besides which the lithological and chemical characters of 

 the Appalachian gneiss are so totally distinct from the crystalline 

 strata of the Laurentian system, with which Prof. Rogers would 

 seem to identify them, that no one who has studied the two can 

 for a moment confound them. Prof. Rogers is therefore obliged to 

 assume a new series of crystalline rocks, distinct from both 

 the Laurentian and Huronian systems, but indistinguishable from 

 the altered palseozoic series, or else to admit that the whole of his 

 gneissic series in Pennsylvania is, like the corresponding rocks in 

 Canada, of palseozoie age.* We believe that nature never repeats 

 herself without a difference, and that certain variations in the 

 chemical and mineralogical constitution of sediments mark suc- 

 cessive epochs so clearly that it would be impossible to suppose 

 the formation in adjacent regions of a series of crystalline schists 

 like those of the AUeghanies contemporaneous with the sediments 

 which produced the Laurentian system. We have elsewhere in- 

 dicated the general principles upon which is based this notion of 



* Dr. Bigsby in 1824 described an extensive tract of gneissoid rocks on 

 Rainy Lake and Lake Lacroix, north of Lake Superior. The general 

 course of the strata he states to be " from N. W. to N. by W., with a 

 corresponding easterly dip ;" but he elsewhere speaks of the gneiss as 

 running (dipping ?) E. N. E. This gneiss often contains beds and disse- 

 minated grains of hornblende, and passes in some places into micaceous, 

 chloritic and greenstone slates, and syenite. Staurotide is abundant in 

 the mica schists, and octahedral iron occurs in the chloritic slates. A 

 porphyritic granite containing beryl is also met with in this region. 

 This gneiss is regarded by Dr. Bigsby as belonging '' to transition rocks, 

 from its constant proximity to red sandstone, the oldest organic lime- 

 stone, and trap." (Am. Jour. Sci, (1) viii, 61). The lithological and 

 mineral characters of these crystalline strata seem to be distinct from 

 those of the Laurentian system, and to resemble those of the Appala- 

 chians. Too much praise cannot be ascribed to Dr. Bigsby for his early 

 and extensive observations on the geognosy and mineralogy of British 

 North America. 



