NOTES ON THE GEODES OF ILLINOIS. 701 
is solid or hollow, and also how hard a blow is needed to break it 
open, if he finds it light enough to be hollow; for a heavy blow, 
such as is necessary to crack a thick crust, would dash a thinner 
one into small fragments. Those large geodes that contain 
much calc spar are usually solid, while those that are smaller and 
lined with small crystals of this material are frequently quite hol- 
low. The quite large specimens are more apt to have thick walls, 
or to be entirely solid, than those of less size whatever the filling. 
The cavity of a geode does not often correspond with the exterior, 
as the walls are constantly varying their thickness. Many are 
lined with a single, plain layer of crystals, others have this crys- 
talline surface raised in rounded prominences, some of them long 
and cylindrical, others low and mound-like. In some, besides the 
lining there is a partition, extending across the cavity, lined with 
crystals on both sides. Rarely, the collector may find a thin crust 
lined with small bright crystals, within which is a hollow ball, but 
little larger than the cavity and attached at one or two points to 
the side, covered with somewhat smaller crystals. So, in innu- 
merable ways do we find these singular objects varied and, as the 
outside gives little or no indication of the inside, the charm of 
uncertainty is added to the excitement and pleasure of the collec- 
tor. So far as my own experience’ goes those specimens that are 
from one to three inches in diameter are least likely to be solid, 
though very fine ones may be obtained six or even ten inches in 
diameter without great difficulty. The range in size is quite large, 
as very pretty specimens not over half an inch in diameter may 
be found, while the largest I have seen were fully eighteen inches 
across the broken halves. But these larger geodes, aside from 
being very scarce, are not very desirable acquisitions as they are 
very heavy, weighing fifty pounds or more in the best examples. 
The geodes are most abundant, and hence most easily collected, 
in the beds and along the sides of those streams which intersect 
the geode bed, as nearly all those around Hamilton and Warsaw 
do. The geodes are dislodged from their resting place by high 
water, frost, ete., and are carried down by the streams, so that 
near the mouth, or in a basin, the ground is often paved with 
them, but good specimens are not rare along the sides of the 
streets, in cuts, or wherever the earth has been washed or dug in 
the neighborhood of the bed in which they lie. Few things are 
more unpromising or unattractive than a geode when first taken 
