420 W. G. Foye — Nephelite Syenites of Ontario. 



Microscopic description. — The thin section of the kaolinized 

 rock shows only a few features not discernible in the hand 

 specimen. 



The calcite is present in large cleavage sections set in a 

 matrix of fine, fibrous, decomposition products consisting of 

 kaolin and muscovitc. 



The muscovite often shows rosette arrangement. 



Fig. 4. 



Fig. 4. Distribution of the several rock types in the Crescentic Laccolith 

 of Tory Hill. 



a= Garnet-pyroxene rock, b=Hornblende-nephelite rock, c=Monrnouth- 

 ite, d= Pegmatitic nephelite syenite, e=Biotite-nephelite rock, /=Granite 

 pegmatite. 



B. The Crescentic Laccolith near Tort Hill. 

 General Geology. 



This laccolith is indicated on the accompanying sketch map 

 (fig. 1) by the letter B ; fig. 4 shows the general distribution of 

 the rocks associated with the body. 



There are two parts to the laccolith. These are separated 

 by limestone. Limestone surrounds the mass on all sides and 

 dips away conformably to the contact. A massive, granite- 

 pegmatite dike forms a hill 200 yards across, south of the 

 body. 



A basic nephelite rock, consisting predominantly of garnet 

 and pyroxene, is found at the lower or northern contact of the 

 laccolith. The contact occurs at the top of a steep hill. The 

 garnet-pyroxene rock forms a zone from four to eight feet in 

 thickness. It grades into another type, still basic, but contain- 

 ing nodules of nephelite and some hornblende. The latter 



