428 ELEMENTARY GEOLOGY 
In England and France, as well as in Texas and Iowa, there 
are also beds of Cretaceous rock composed of extremely minute 
forms of life, producing the well-known chalk. These strata were 
formed in the deep sea of this period, by minute animals that 
swam at the surface, and upon death dropped to the bottom, form- 
ing an ooze quite like the Globigerina ooze (p. 257) now accumu- 
lating in the depths of the sea. 
Fig. 246. 
A group of Cretaceous fossils. 
(1, Hippurites radiosa; 2, Pecten equivalvis; 3, Toxaster elegans; 4, Gryphea 
vesicularis (an oyster) ; 5, Ananchytes ovatus.) 
A noticeable development is also seen in the fishes ; 
but the characteristic Mesozoic fish is still of the ancient 
armored type, mentioned in the description of the Pale- 
ozoic life. 
