79 



The stream, in its somewhat tortuous course, 

 flows with a gentle current between low banks 

 of drift and alluvium. In places the under- 

 lying crystalline limestones with associated 

 alkaline syenites outcrop, but there are com- 

 paratively few exposures in the immediate 

 vicinity of the river banks. For a distance of 

 nearly 17 miles (27-3 km.) from Bronson's 

 Landing to the head of Foster's rapids, there is 

 uninterrupted and comparatively deep water 

 suitable for the passage of canoes and other small 

 craft. 



The Occurrence of Dungannonite. 



In the Township of Dungannon, Cons. XIV and XV, 

 lot 12 is the locality from which the original dungannonite, 

 a corundum-bearing alkali syenite with accessory nepheline, 

 was obtained. 



The typical dungannonite contains nepheline only 

 in small amount and as an accessory constituent. Asso- 

 ciated with it in the same series of exposures, however, 

 there are differentiation phases of the magma which are 

 rich in nepheline, the nepheline syenite thus resulting 

 having as its essential constituents nepheline, plagioclase 

 and biotite. This rock in places contains dark basic 

 patches which are rich in hornblende, as well as others of a 

 yellowish colour which contain an abundance of scapolite. 

 The whole series has a well-defined foliation striking 

 N. 25 E. 



The dungannonite under the microscope is seen to be 

 made up largely of plagioclase having the composition of 

 andesine. Next to this feldspar corundum is the most 

 important mineral constituent. Scapolite is also present, 

 usually in subordinate amount, the larger individuals 

 occupying the interspaces between the feldspars. Biotite 

 is present in small amount, while muscovite occurs both 

 intergrown with the biotite and as mantles of variable 

 width surrounding the corundum individuals. This mus- 

 covite is regarded as a primary constituent formed at a 

 time immediately preceding the complete solidification of 

 the magma. Occasional grains or imperfect crystals of 

 magnetite, with a small amount of calcite, complete the 



