120 ANIMAL ACTIVITIES. 
bonate or limestone. When these shells are perforated 
with many holes the animals are called Foraminifera. 
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Fic. 102.— One of the Foraminifera. 
Some of these foraminifera have been found of large 
size and in such great numbers that their fossil remains 
make great deposits of limestone. 
Fic. 103.—The Origin of Chalk. A, chalk (magnified); B, ooze (mag- 
nified). 
Chalk. At present there live near the surface of the 
ocean great numbers of these shelled Rhizopods. 
