SOUTHERN CALIHORNIA ACADEMY OF SCIENCES 15 
Figure 4 gives an idea of the variety of size and form of 
diatoms. 
Diatoms are found singly or in colonies; free or attached; 
in hot or cold, fresh or salt water, recent or fossil, all over 
the world. Their motion is deliberate, in marked contract 
with the irritable impatience of the Infusoria, which are their 
pond companions. One boat-shaped diatom called Navicula 
(of which there are two or three hundred species), is so abund- 
ant in all fresh water pools and ponds that nearly every 
microscopic mount shows a quantity of specimens and often 
several species. 
These fairy brown fleets go moving across the field, sailless 
and rudderless, with a steady and gracefully easy motion. 
If perchance one meets with an obstruction, a bit of alge, fibre 
of wood, or grain of earth, it bumps against it obstinately 
several times, then, convinced that its Northwest passage is 
blocked, it backs off and sails backward with equally delibe- 
rate dignity. 
One odd species is called Bacillaria paradoxa. Its motion 
is most peculiar. This Bacillaria is composed of numerous 
rod-like pieces that can move upon each other, and it has the 
power of attaching itself to objects. Slowly across the field 
may be seen extending a jointed rod, its parts sliding past 
each other like a sliding ruler, till it attains its full length. 
Then the pieces slide backward, and, an arch, or zig-zag fig- 
ure, or pontoon bridge is formed, the arrangement varying 
constantly with the ceaseless motion, till one is weary of watch- 
ing. This peculiar species was abundant on Flower street, 
back of the State Normal School, before its ocean was drained 
and dried up for the good of the publi. 
The siliceous shells of diatoms are practically indestructible, 
and consequently they are an important item in world build- 
ing. They are found in all geological strata as far back as 
the Devonian, and probably, much of the amaphous silica of 
the Silurian Age was at one time diatom shells. The fossil 
deposits are called diatomaceous earth. 
Abundance of Diatoms. 
These plants must have existed formerly in inconceivable 
numbers, for their remains form extensive beds of miles in 
extent in almost every country of the world. 
The earth is abundant in California, and all states of recent 
geologic formation. ‘‘The city of Richmond, Va., is built on 
such a deposite, from two to eighty feet thick and several 
miles in extent.’’ The city of Los Angeles has its share. There 
is a large area of this earth under the court house, another 
