108 Dr. Mac Culloch on the 



and not less in the proportion which these bear to the feldsjpar ; 

 although they are generally in much inferior quantity. It also 

 varies in colour, being of a very pale green, of a darker hue 

 of the same, of a pale grey, of a dark grey nearly approaching 

 to black, of a brown and of a purplish brown. 

 . The feldspar is sometimes compact, or very finely granular ; 

 both of these appearing to be modifications of compact feld- 

 spar. In either example it is compactly platy, and at the same 

 time irregular ; while it is occasionally also perfectly platy, as 

 is the mineral called common feldspar. In a few instances it 

 approaches to the glassy variety. The colour is either a greenish 

 white, or pale ochry, or pure white; and, in some rare in- 

 stances, it is brown, grey, and purplish brown. 



It is easy to understand therefore, how, from the varying 

 tints of these two essential minerals, their varying proportions, 

 and the various magnitude of the parts, the colours, and ge- 

 neral aspect of this rock may vary, and it is unnecessary, 

 therefore, to dwell on this part of the subject. I may only add, 

 that where mica, or quartz, or any of the other minerals above 

 named, are present, they produce varieties which may readily be 

 investigated, and on which it is unnecessary to dilate further. 



The following synopsis contains a brief view of the varieties 

 which have fallen under my notice ; including, for the present, 

 that which consists of diallage and serpentine. 



Synopsis of Diallage Rock. 



First Division. Simple, or composed of Diallage alone. 



A. A confused mixture of crystals of diallage. 

 The aspect of this rock varies materially according to the 

 magnitude of the crystals ; and it appears rather to form veins 

 or concretions in the mixed rock, than to occur in distinct masses 

 or strata. 



Second Division. Composed of two Ingredients. 



A ^A mixture of diallage and feldspar. 



a. Diallage and platy feldspar. 



b. . Dialla geand fine granular feldspar. 



c. Diallage and compact feldspar. 



