116 WORMS, MOSS-POLVPS, 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. But a 

 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 



