142 TRANSACTIONS OF THE [FEB. 19, 
especially ina polished slab. In the nodule figured in PI. IT. these 
are exceptionally large. In others they are less pronounced. 
Toward the rim the biotite in irregular shreds begins to be 
noticeable, and the nodule is more finely crystalline. Still 
further the biotite begins to assume a eoncentric arrangement, 
which is very pronounced, and much magnetite is associated 
with it in rather rough octahedral cry stals. After a very de- 
cidedly darker zone the inner part of the nodule ceases ab- 
ruptly. It is this portion that separates easily when the rock 
is broken up. There remains, however, outside of each core a 
marked rim or outer zone. This is 2 to } inch (8-6 mm.) wide, 
and is formed of plagioclase crystals with their twin lamelle 
radiating from the inner portion. All the crystals, it should be 
stated, have not the lamelle sharply radial, for the twin sections 
show at times some irregularity, but as a ‘rule they are in this 
position and in sufficient numbers to give a strong impression 
of radial arrangement. The effect is heightened by a fine dust 
of magnetite that is sprinkled through them, but with sugges- 
tions also of the same concentric alignment So pronounced in 
the internal, dark zone. The rim ends sharply against the 
granite of the matrix, which is in all respects normal. In one 
portion, the outer rim of the nodule in the upper right hand 
corner of the plate is interfered with by a group of rather 
coarser crystals than the general matrix, but in all other cases 
seen it is entire. The coarser group is probably an incipient 
nodule. Some nodules are more thickly sprinkled throughout 
with dark minerals than others, and such are shown in the 
half tone plate of a large block. 
In this curious structural anomaly we evidently can observe 
the following facts: (A.) A much more basic aggregate of 
minerals is present in the spheroids than in the normal granite. 
(B.) In the individual spheroid the innermost core is most 
acidic; it shades into the most basic portion of all next the 
outer rim; the outer rim is of medium basicity. It is equally 
clear that in the still fluid magma centers of crystallization 
began, consisting of plagioclase (i. e. oligoclose), with subordi- 
nate quartz and orthoclase. The expanding centers occasionally 
involved with themselves biotite and magnetite, which were 
doubtless already formed in the magma. As the nuclei grew 
increasing amounts of biotite and magnetite were entangled or 
drawn in by a concretionary action until they were nearly ex- 
hausted in those portions of the magma neighboring to the 
nuclei. Finally the rim formed. While yet soft the spheroids 
were more or less flattened, probably by movements in the 
magma. Much the same process has been outlined for the other 
