ELISHA MITCHELL SCIENTIFIC SOCIETY 62 
is full of nodules of various shapes and sizes, ranging from 
that of a pin’s head to nearly two inches in diameter. These 
are the supposed concretions and fossils, Upon a fresh frac- 
ture the rock appears to be composed chiefiy of quartz, but 
when weathered most of the nodules become white as if kaol- 
inized, while the other nodules and tne matrix remain quart- 
zose in appearance. ‘The nodules form at least two-thirds of 
the mass of the rock and are arranged with their longer 
diameters parallel, rendering the rock rather easily split in 
one direction. 
With a lens, it may be seen that the small kaolinized 
nodules exposed in section upon the surface of a hand speci- 
men have a radial fibrous structure. The same structure 
may be seen in some of the larger ones, and in addition to 
this feature some of the nodules possess a more or less dis- 
tinct concentric shell-like structure. These structures are 
usually best displayed upon or close to a weathered surface. 
Portions of the nodules or spaces between them are in a few 
cases cellular, and the walls of the openings are rarely lined 
with minute crystals. The supposed fossil forms usually 
appear conical or discoidal upon a weathered surface. They 
often show a small cup in the apex and are surrounded by a 
narrow depression from which the radial fibrous envelope, 
pointed out by Mr. White, has been removed by weathering. 
A careful comparative study of the nodules in the hand 
specimens tends to convince one that however different in 
form and size the supposed fossils and concretions may ap- 
pear, all belong to one series and have essentially the same 
origin. 
A microscopical study of thin sections of the rock reveals 
the fact that the nodules are spherulites, a common feature 
of acid igneous rocks. ‘They «re composed in most cases 
chiefly of fibrous feldspar with quartz or tridymite. As seen 
in the thin section of the Paleotrochis-bearing rock, the fibres 
are grouped radially with more or less irregularity in tufts, 
sheaves, sectors, hemispheres or spheres. When they forma 
complete sphere, which is rarely the case, they are most 
