1908 ] 
Journal of the Mitchell Society 
73 
fracture across the foliation of a biotite crystal. Monazite occurs 
in contact with the various minerals of the sectoin, though it is 
more commonly surrounded by or included in grains of biotite and 
quartz. The position of the monazite in the biotite indicates 
replacement, and the biotite foliae are not displaced around the 
crystals. In the microscopic sections sufficient feldspar was not 
observed to determine its relation to the other minerals. 
The rock has been so thoroughly recrystallized that it is diffi- 
cult to give the relative order of formation of the minerals. Bio- 
tite, if not still in its original condition, was probably the first 
mineral to form during recrystallization. Part of the graphite 
was probably contemporaneous with the biotite. Some, however, 
was introduced later and formed at the same time with the quartz. 
The small amount of muscovite in the rock was probably next to 
form, followed closely by quartz. From the small amount of 
; feldspar in the microscopic sections, it was not possible to state its 
relative period of formation. From the hand specimen, however, 
it is evident that the feldspar was introduced later than the quartz, 
or possibly contemporaneously with part of it. 
Origin 
The occurrence of monazite in granitic and pegmatitic rocks indi- 
cates that its origin is associated with magmatic agencies. It is 
probable that the constituents of monazite are associated with gran- 
| itic magmas and that only part of the mineral crystallizes out 
when such magmas solidify. During the formation of pegmatite 
■! magmas and solutions from the residues of the solidification of 
granite part of the constituents of monazite are retained. When 
these pegmatite magmas and solutions are intruded into or depos- 
: ited in the gneisses and schists in masses such as are mined for 
mica, monazite forms in large masses or crystals. During 
j the pegmatization of rock formations by these magmas and solu- 
[ tions the monazite is carried into the gneisses and schists where it is 
now found. This pegmatization with which monazite is associated 
: was probably produced by the passage of active magmatic solutions 
Ij through the rock, both aiding in recrystallization of the original 
y constituents, and depositing the materials held in solution when 
[I conditions of temperature or agents of precipitation were favorable. 
