188 MINERALS AND GEOLOGY 



Compact varieties of Hornblende Rock and other hornblendic 

 examples of the Metamorphic Series. 



Diorite is the name commonly given to a granitoid trappean rock 

 made up of more or less distinctly visible grains or imperfect crystals 

 of a soda-feldspar (or lime-feldspar) and hornblende, and containing 

 very frequently, in addition, small grains of carbonate of lime, 

 particles of magnetic iron ore, scales of mica, sphene, and other 

 minerals. It passes into compact greenstone by almost insensible 

 transitions ; and in many cases it cannot be distinguished readily, if 

 at all, from varieties of dolerite or granitoid trap. Its feldspathic 

 portion is usually white or grey, or sometimes reddish, and the horn- 

 blende black or green ; but fine-grained examples have very 

 commonly a distinct green colour throughout. Massive, slaty, 

 columnar, amygdaloidal, and porphyritic varieties occur, as in other 

 kinds of trappean rock. The specific gravity varies from about 

 2.6 to 2.9. 



Examples of diorite, of a more or less granitic aspect from the 

 frequent presence of small scales of brown mica, occur in the eruptive 

 masses of Belceil, Monnoir or Mt. Johnson, Rigaud, and Yamaska, of 

 the Eastern Townships of Canada. Other examples, passing here 

 and there into diabase, are seen at several spots on the shores of 

 Lake Superior, as near Michipicoten Harbour and elsewhere in that 

 neighbourhood, Batchewahmung Bay, &c. The term diorite, it must 

 be remembered, has also been applied by certain authors to some of 

 the stratified hornblendic rocks of the Metamorphic Series these 

 crystalline strata representing, as regards general composition, many 

 diorites and other intrusive rocks containing hornblende, just as the 

 gneissoid strata represent the granites and syenites. To avoid con- 

 fusion, however, the term if employed at all, should be restricted, in 

 accordance with common usage, to intrusive or eruptive rocks. If 

 the same term is to be applied indefinitely to a stratified and eruptive 

 form of rock, it follows logically that the term gneiss should be 

 abandoned, and all the micaceous examples of gneiss should be 

 known as granite, and the hornblendic varieties as syenite a system, 

 we presume, that few geologists, apart from those of a certain school, 

 would be inclined to follow. 



Diabase or Chloritic Trap as defined by most authors is an 

 eruptive, feldspathic rock, containing augite or hornblende with a 



