The chalk was deposited at the bottom of a great inland sea that covered most of North America during the later part of the Cretaceous Period, about 80 million years ago.
(The chalk; was deposited; at the bottom of a great inland sea) (a great inland sea; covered most; T:during the later part of the Cretaceous Period, about 80 million years ago)
The chalk a great inland sea
was deposited covered most
at the bottom of a great inland sea
T:during the later part of the Cretaceous Period, about 80 million years ago