40 SYDNEY H. BALL 



accessory minerals are titanite, magnetite, apatite, and fluorite. 

 Fluorite flecks the alkali feldspar and was probably introduced by 

 magmatic gases. 



The soda-syenite is cut by dikes of a compact greenish-gray 

 aplite. Pink feldspar is associated with the gray feldspar, and some 

 veins are composed wholly of pink feldspar with pyroxene. Under 

 the microscope the aphte has a very uneven-grained, allotriomorphic 

 texture. The feldspars include microperthite, orthoclase, and some 

 anorthoclase ; a httle quartz is also present. Although the rock 

 is not rich in ferromagnesian minerals, there are many small grains 

 and partial crystals of aegirite-augite, which show the usual zonal 

 structure, with deeper green bands on the border. Irregular grains 

 of a light-yellow garnet are rather abundant and titanite and apatite 

 are accessories. Fluorite occurs in small blebs, surrounded by a 

 mesh of sericite shreds, which were probably formed by the same 

 gases that deposited the fluorite. Calcite is also present and its 

 contacts with other minerals are so sharp that it was probably deposited 

 in miarohtic openings. The contact between the aphte and the 

 syenite is in some cases sharp, in others gradational. In one instance 

 a dike of syenite porphyry is faulted along an aphtic dike, but there 

 is httle doubt that the two are genetically related. Narrow pegmatitic 

 dikes, the feldspar and pyroxene of which reach a diameter of i inch, 

 also occur. 



The soda-syenite intrudes Pennsylvanian hmestone and has suf- 

 fered the same deformation as the quartz-monzonite which hes to the 

 south of it (No. II, Table I). Phases of the pegmatite of the mon- 

 zonite closely resemble the soda-syenite in mineral composition and 

 from this fact and the proximity of the two masses the soda-syenite 

 is beheved to be a later differentiation of the monzonitic magma. 

 At places the pegmatite of the monzonite has a border composed of 

 almost pure augite with a median band of feldspar. The boundary 

 planes are rather distinct although individual crystals extend from 

 the monzonite into the basic bands and from these into the acidic 

 center. The more sihceous portion shows under the microscope the 

 composition of a soda-syenite, and consists of orthoclase, anortho- 

 clase, augite, hornblende, ohgoclase, quartz, titanite, magnetite, 

 apatite, and zircon. Titanite occurs both in well-crystalhzed wedges 



