116 WORMS, MOSS-POLYPS, SPONGES, ETC. 
tions, and soon reducing them to powder. Such 
sponge-bored shells and rock-fragments may be 
readily recognized by the numerous small holes 
that open upon the surface. 
FORAMINIFERA. 
Still lower in the scale of organization than the 
sponges are a number of animal forms whose exist- 
ence is not very generally suspected by the visiting 
public. We walk leisurely over the sands, little 
suspecting that in so doing we may be ruthlessly 
crushing to powder thousands of minute shells that 
lie buried beneath our feet. To the ordinary ob- 
server the sand appears to be a mass of nearly 
homogeneous particles, little granules of white 
and black quartz, through which are scattered at 
intervals scales of mica, and exceedingly minute 
fragments of another mineral known as _ horn- 
blende. These are all derived from the destruc- 
tion of certain rock-masses—the granites and their 
allies principally—situated somewhere within the 
continental border, and merely accumulated by the 
sea after it has received the products of destruction 
from the various rivers discharging into it. Buta 
more critical examination of the sand shows that in 
addition to the mineral substances above mentioned 
it contains at times—and it may be said, at almost 
all times—great quantities of tiny rounded shells 
whose dimensions barely exceed those of the sand- 
particles themselves. Without the aid of a magni- 
fier these shells are almost undistinguishable; but 
the lens and a practised eye will soon pick out the 
