32 Fi—ELD CoLUMBIAN MusEumM-—Geotocy, Vot. III. 
A series of 32 specimens received later confirms the characters of 
the earlier lot. They include a number of globular specimens which, 
however, have the same structure as the rosette forms, from which 
they differ in the number and dimensions of the component plates. 
That is, the globular forms are merely thick rosettes.: One specimen 
consists of a group of many nearly globular forms enclosed in the 
weathered matrix which assumes the form of a red sand. This sand 
appears to be the residue left from solution of the limonite cement of 
a ferruginous sandstone. | 
The rosette appears upon both sides of an approximately octa- 
gonal plate which may be designated the basal plate of the aggregate. 
This is penetrated obliquely by a variable number of similar plates. 
which appear to intersect at the centre of ‘the aggregate and project 
on both surfaces. These plates make angles of approximately 30° 
with the bases. While these plates appear as if passing through 
the basal plate and any important one appearing on one side 
may be readily discovered on the other, yet the two rosettes are 
never exactly alike. One is always more complex than the other and 
formed of smaller plates. These plates generally, but not always, lie 
in a confusedly whorled position. ‘They are not simple but frequently 
consist of two plates inclined to each other at angles of approximately 
30° and intersecting some in the vertical and some in the horizontal 
plane. By repetition of this compounding of plates, always at 
angles of approximately 30° so far as the roughness of the 
material will allow determination, the apparently irregular orientation 
of the leaves of the rosettes may be accounted for. By a greater 
degree of this compounding also is the greater complexity of one face 
over the other produced. The specimens, examined detail by detail, 
are decidedly unsymmetrical, yet when the broader features only are 
considered, symmetry of a high order is present. ‘The rosettes on 
either side of the basal plate while not identical in detail are so in 
mass, and proportioned so that the aggregates are symmetrical with 
respect to the plane of the basal plate, as well as to a central axis at 
right angles to this plane. There is also a tendency in some of the 
specimens towards an axis of hexagonal symmetry in the plane of the 
basal plate. The secondary plates appear to so twist as to all intersect 
along this axis. 
The position of those portions of the plates which lie buried in 
the body of the specimen may be followed by the cleavages upon the 
fractured surfaces. From an examination of these cleavages it 
becomes evident that the plates do not really intersect or interpene- 
