OF CENTRAL CANADA PART III. 180 



certain amount of chlorite : carbonate of lime being very generally 

 present as an additional constituent. The term " diabase " is often 

 applied, however, to chloiitic and other varieties of hornblendic and 

 augitic rocks belonging to the Metamorphic Series. Some kinds of 

 eruptive diabase have also been described as melaphyre, but this term 

 is also vaguely applied to many diorites and other granitoid rocks of 

 the present group. Compact varieties, which are mostly of a decided 

 green colour, pass into compact trap and greenstone by insensible 

 transitions. Granitoid varieties merge also into dolerite and diorite. 

 Both kinds offer amygdaloidal, prophyritic, and other examples. 

 The feldspar in coarse-grained examples is either greyish- white, 

 greenish, reddish, or brownish ; and the chlorite presents the form of 

 small scales and particles of a green colour. Weathered examples are 

 usually dull-brown or red. Varieties of diabase, as thus denned, 

 occur both in the form of dykes and in intercalated bedded masses 

 among the Huronian strata of Lake Superior, as in Michipicoten 

 Island, as well as Cros Gap, Cape Maimanse, Point-aux-Mines, 

 Goulais River, and elsewhere. The bedded examples may perhaps 

 be really metamorphosed strata, but they consist most probably of 

 portions of ancient trappean overflows formed during the gradual 

 building up of the Huronian deposits. Some contain epidote ; 

 others enclose well-defined crystals of augite ; and many are in the 

 condition of calcareous amygdaloids. 



Trachytes : The rocks of this division are essentially feldspathic 

 in composition, the more typical or charactaristic examples consisting 

 almost wholly of orthoclase or potash-feldspar. Many of these are 

 more or less porous or vesicular in texture, and are thus peculiarly 

 harsh or dry to the touch, when the name " trachyte," from rpa^b^^ 

 rough. This character, however, will only apply to certain varieties, 

 as many trachytes do not differ in this respect from other rocks, 

 Most trachytes are white, light-grey, or pale reddish in colour ; but 

 in the granitoid varieties the presence of scales of brown mica, small 

 crystals or particles of green or black hornblende, and other accessory 

 minerals, gives rise to a darker and variable tint. These trachyte 

 rocks merge into members of the granitic and trappean series on the 

 one hand, and into ordinary feldspathic lavas on the other. The 

 substance known as pumice, for example, may be referred both to 

 trachyte and to lava. Thus, many trachytes, occuring in connection 



