• RESUME AND CONCLUSIONS. 359 



mineral constituent recognized. This rock resembles closely the black, 

 coarse dikes which are found in connection with several of the intrusive 

 mountains of the eastern townships. 



Of the pyroxenic and feldspar dikes it may be said that in earlier re- 

 ports they are described as integral portions of the gneiss formation. In 

 places they extend along the lines of bedding, and are of the nature of 

 bedded dikes, but in others they cut transversely across the strike of the 

 gneiss, and their intrusive character is further established by the dis- 

 placement and alteration of the strata in contact and by the formation 

 of crystals of various kinds. The effect of the intrusion of the pyroxene 

 upon the occurrence of economic minerals as well is easily seen at many 

 of the apatite mines of the Buckingham district, and upon the establish- 

 ment of their intrusive character the occurrence of the phosphate is more 

 readily explained. It has been found by careful examination at many 

 points that this apatite occurs, not in the gneiss itself, but in the mass of 

 the intrusive pyroxene dikes ; and, further, that its presence in workable 

 quantity is always near the contact of the dike with the gneiss. Occa- 

 sionally apatite is found in the limestone overlying, but only in detached 

 crystals, along with pyroxene and mica and graphite. The same effect 

 is visible in the occurrence of the mica and graphite, the workable de- 

 posits of which arc cither in the mass of the intrusive rock or in the 

 gneiss and limestone adjacent. 



Resume and Conclusions. 



Reviewing, then, briefly the conclusions as to structure arrived at by 

 the writer, the succession, in ascending order, in the district under con- 

 sideration, may be thus stated : 



1. Reddish-gray gneiss without distinct signs of bedding or stratifica- 

 tion, hut with a foliated structure. In connection with this are great 

 masses of syenite-gneiss and augen-gneiss, in winch foliation is for the 

 most part entirely wanting, and much of which is presumably intrusive. 



2. Reddish orthoclase gneiss, interst rati tied with black hornblende, 

 grayish quartzose and garnetiferous gneiss, with beds of grayish quartzite, 

 and rusty may, often highly quartzose, gneiss, the whole showing a well- 

 stratified arrangement of beds, generally with very distinct appearance 

 of sedimentation, many of the beds in the upper part having the aspect 



, of regularly deposited layers of quartzose sandstone. 



•'!. The grayish and rusty gneiss passes upward gradually into the cal- 

 careous portion of the system, thin bands of limestone first appearing as 

 interstratified beds along with the gneiss, the intcrstratification becoming 

 less as we ascend the scale, till, through scattered, twisted inclusions, the 

 gneiss disappears and the rock becomes a regular crystalline limestone, 



