Natural Formation of Pellets. — TJdden. 
269 
the same material as that of the matrix in which they are lodged. 
Breaking them open they are seen to have an outer dense crust and 
a loose, porous interior. (Fig. 2.) The thickness of the crust av- 
Fig. 2. 
Fig. 1. 
Fig. 1. Exposure of tiie volcanic dust near the N. E. corner of Sec. 14, T. 18 S., 
R. 3 W., McPlierson county, Kansas. l,Soil; 2, Indistinctly ripple-bedded upper 
part of the deposit of dust; 3, Ripple-bedded, with pellets; 4, Not ripple-bedded, 
and with casts of the leaves and stems of sedges; 5, Fine, jointed clay. 
Fig. 2. A pellet. 
Fig. 3. Flakes of volcanic dust. A, Flake with a branching rib on one side; B, 
Broken hollow sphere of volcanic glass, with a vertical plate (rib) on the outside; 
C, Fragment with cavities drawn out into fine tubes ; D and E, Plain fragments of 
broken spheres. 
erages in thirty specimens about one-seventh of the total diameter, 
but it varies from one-fifth to one-seventeenth of the same. As a 
rule it is uniform all around, but occasionally it is thicker on one 
side when the outer surface appears to bulge out. Examined un- 
der the microscope it is seen to consist of pumice fragments of 
only the most minute size. A gradual change from the very finest 
material in the outer part of the crust to larger fragments on the 
inner side, can alwa3S be noticed. Occasionally the entire crust 
will separate into two or more concentric laminae. 
The interior of the pellets is filled with particles of large size,^ 
averaging considerably above that of the dust in which the pellets 
are imbedded, and loosely placed in the cavity of the crust without 
any particular arrangement. They do not quite fill the space within 
the crust. In some cases unbroken hollow spheres of volcanic 
