in Norway and in Canada, 17 



to be conformable with tbe more distinctly banded portion of the 

 strata." {Ibid, p. 9-10.) 



Besides gneiss, the following rocks are mentioned as occurring 

 in the Laurentian system. A crystalline aggregate of feld- 

 spar and quartz, granite in veins, mica and hornblende schists, chlo- 

 ritic gneiss, quartz-rock or quartzite, hypersthenite, serpentine, 

 crystalline limestone, greenstone, hornblende rock, besides syenite 

 and porphyry, which latter intrusive rocks however belono- to a 

 later period. These rocks are, on the whole, the same as those 

 occurring in the primitive gneiss formation of Norway. Granite 

 however does not seem to occur iu masses running parallel with 

 the other rocks, unless we include under this denomination the 

 above mentioned crystalline aggregate of feldspar and quartz. 

 The hypersthene rocks described by Mr. Hunt in his inte- 

 resting Report 1855, seem to be of a character similar to 

 those occurring in Norway, and there described as gabbro and 

 euphotide, however much the latter rocks, in their true types, 

 differ from hypersthenite. The confusion existing among mine- 

 ralogists regarding the nature of these rocks seems still to prevail^ 

 notwithtanding the able and exhaustive work of Mr, Hunt on the 

 subject. As a proof of this, I may refer to a recent paper by 

 Dahll on the ore district of Kongsberg, where there is a rock 

 described as gabbro, which is composed of " violet or brownish 

 labradorite and dark green hornblende. The color is that of the 

 hornblende, consequently dark. Diallage, which is known by its 

 shining lustre, is perhaps oftener present than has hitherto been 

 demonstrated ; ilmenite is characteristic ; and magnetic pyrites oc. 

 curs frequently ; with these, a little brown mica is frequently re- 

 marked." Oni Kongsberg^ s Erts District, p. 16, Gabbro is 

 commonly described as " a crystalline, granular or sometimes 

 schistose mixture of feldspar or saussurite with diallage orsraarag- 

 dite ;" Cotta : Gesteinslehre, p. 53. It is diflScult to conceive how 

 the above described rock resembles gabbro ; unless as Dahl furth- 

 er remarks concerning it, "labradorite is decisive of gabbro."* 



(Editor's note, by T. Stebry Hunt.) 



* The name of gabbro, originally employed by the Italians to desig- 

 nate a diallagic serpentine, is, by most modern authors, applied to a 

 rock composed of a tricliuic feldspar (such as labradorite) with pyroxene. 

 When the latter is of the variety called hypersthene, the rock takes the 

 name of hyperite or hypersthenite, but when it assumes the form of dial, 

 lage or of smaragdite, the name of gabbro is given to the rock. In smar- 

 Can, Nat. 2 ^ Vol. VU. 



