

W. G. Foye — Nephelite Syenites of Ontario. 419 



masses of scapolite, 2-3 cm. wide, are irregularly distributed 

 through the rock, and, here and there, a bit of pyrrhotite is 

 seen. 



A delicate pinkish white mica is also present and areas of 

 sodalite which fade gradually into the nephelite. 



The rock is allotriomorphie granular in structure, breaks 

 with an irregular, subconchoidal fracture and is very fresh in 

 appearance. 



Microscopic description. — The microscope shows that neph- 

 elite, sodalite and calcite predominate in the pegmatite. 



The nephelite is in amoeboid forms extending into the albite. 

 The evidence seems to show that whereas albite replaced 

 microcline in the canadite, due to the increasing amounts of 

 soda in the syenite magma, in this case the albite was replaced 

 by nephelite for a like reason. 



Sodalite, also, replaces the nephelite and wraps about the 

 grains of the latter mineral in irregular, amoeboid granules. 



The albite is practically free from lime. It is present in 

 anhedral granules with threads of calcite intergrown along its 

 twinning planes. 



The order of crystallization is muscovite, calcite, albite, neph- 

 elite, sodalite. 



4. Kaolinized Contact Hock. 



Macroscopic description.- — There is a gradual transition from 

 the nephelite pegmatite to the limestone along the upper con- 

 tact of the nephelite syenite laccolith. The nephelite peg- 

 matite is gradually altered to kaolin and calcite becomes more 

 abundant until it completely replaces the nephelite rock. 

 Biotite and apatite with minute red garnets appear, together 

 with large masses of granular scapolite and albite. 



Twenty per cent of the rock is nephelite. This mineral is 

 altering to kaolin, which forms fifty per cent of the rock. Cal- 

 cite occurs in resorped grains in the nephelite and kaolin. 



Apatite occurs as prismatic crystals 1-2 cm. long and a cen- 

 timeter wide. The mineral is a light apple-green in color. 



The kaolinized and the fresh pegmatite are equally exposed 

 to the processes of weathering. The kaolin is, therefore, prob- 

 ably not due to secular alteration. The presence of fresh cal- 

 cite within the kaolinized rock, also, would indicate that secular 

 weathering has not progressed very far and that the solutions 

 which effected the kaolin ization did not contain acids capable 

 of corroding the calcite. It is believed that the kaolinization 

 was produced by carbonated waters during the latter part of 

 the period of pneumatolytic action which produced the nephel- 

 ite pegmatite. 



