GEOLOGY OF THE I>ORT LEYDEN QUADRANGLE I9 



are quartzose and garnetiferous may be accounted for by some 

 such process. 



Three syenite-Grenville areas are shown on the map. The 

 largest of these extends from Denley station to north of Greig, 

 a distance of nearly 12 miles, while the width averages some- 

 thing like 3 miles. In the southern portion of this area the 

 Grenville is present in greater force than the syenitic or granitic 

 rocks, while in the northern the reverse is true except possibly 

 in the vicinity of Greig. Within this area there seems to be good 

 evidence for the former existence of very ancient Grenville rock 

 belts or structure lines which extended in a northeast-southwest 

 direction. Thus pyroxene gneisses are found in the area east 

 of Fowlersville ; in small outcrops ij^ miles east of Port Ley- 

 den; and i^ mil^s north of Denley, and these are all arranged 

 along a northeast-southwest line. A belt of feldspar-garnet 

 gneisses shows a similar strike and extends from Lyonsdale to 

 Port Leyden. Quartz-sillimanite rocks much like those at Kos- 

 terville have been noted in small exposures from ^ to ^ of a 

 mile north of Port Leyden and this suggests another northeast- 

 southwest belt. A less well defined belt is garnetiferous and 

 passes through Lyons Falls. Still another belt, in which garnet- 

 sillimanite gneisses are commonly found, passes northeast and 

 southwest through Greig. It seems pretty certain that before 

 the intrusion of the syenite, these Grenville belts were continu- 

 ous and well defined and that as a result of the intrusion they 

 were all cut up leaving only here and there masses of the pure 

 Grenville. 



Of the two smaller syenite-Grenville areas, one lies about 2 

 miles north of Fowlersville and the other around East Martins- 

 burg. These rocks are quartzose syenites often containing gar- 

 nets and more or less intermingled with Grenville. 



The great variety of rock types making up this complex and 

 their gradations from one type to another make it difficult to 

 give a proper idea of them by description. Microscopic study 

 of numerous thin sections shows the presence of all the minerals 

 of both the Grenville and the syenite and in addition to them 

 microcline which often occurs as a prominent feldspar. The fol- 

 lowing brief descriptions include most of the leading types : 



I Syenitic facies. These are often practically indistinguish- 

 able from the normal syenite. They are usually, however, pretty 

 fine grained and under the microscope nearly always show a 

 highly cataclastic structure. They frequently contain microcline 



