Chapter 6 
CENOZOIC HISTORY 
AUIS IN IMAM RNG 21D IROND) 
Rock formations and life of the Tertiary The Mesozoic closed 
and the Cenozoic opened with the uplift of the great Cretacic pene- 
plain. Before the uplift, the sea spread over the Long and Staten 
Islands region, but for a time after the uplift the land was there 
high enough to exclude the sea and New York State was wholly 
above sea level. This we know because the. lowest (earliest) Ter- 
tiary deposits do not occur on Long or Staten Islands or in northern 
New Jersey, and hence the region must have been above water. 
The subdivisions of the Tertiary, from oldest to youngest, are 
known as Eocene, Miocene, and Pliocene. The early Eocene de- 
posits are missing from the northern Atlantic Coastal plain, and 
on Long and Staten Islands we have no evidence that any of the 
Eocene is present which thus leads to the conclusion that all south- 
eastern New York was dry land during the whole of the Eocene. 
During the Miocene there was enough sinking to allow the sea to 
encroach over the Long and Staten Islands districts as well as the 
whole northern Coastal plain. Except for very slight oscillations 
of level which we shall here disregard, the region remained: sub- 
merged under shallow sea water during all the Miocene and Plio- 
cene, or till the close of the Tertiary period. The Tertiary deposits 
were sands, gravels, and clays which formed layer upon layer in 
. the shallow sea along the margin of the continent (see figure 22), 
but on Long and Staten Islands they are seldom seen because of 
the more recent covering of glacial deposits. They are finely 
exposed in the Coastal plain of New Jersey. 
The Tertiary period is generally called the “ Age of Mammals ” 
because, although mammals began in a small way in the Mesozoic, 
they became the dominant feature of life for the first time in the 
Tertiary. In the early Tertiary the mammals were very different in 
appearance from those of the present, a common form then being 
a generalized or ancestral type (for example, Phenacodus) about 
the size of a dog and having five toes. Many of our modern mam- 
mals have descended from this type. During the Tertiary the 
mammals developed very rapidly so that by the close of the period 
they were very much as they are today except that man, the highest 
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