Look at the layers of the structure.  They are one on top of the other.  How do you think they formed?  Hint - remember sedimentary rock.

A place called Smoky Hill Chalk in Kansas used to be covered
by a huge sea.

What do see through  the middle of North America? Between 87 and 82 million years ago, a shallow inland sea (the Western Interior Sea) covered most of the Midwest from the Gulf of Mexico to the Arctic Circle.  The Western Interior Sea, sometimes called the Inland Sea, was probably less than 600 feet deep and had a relatively flat and soft, mud bottom. Near the middle of the seaway where Kansas  is now located, sediments were deposited at a rate which would ultimately produce about one inch  of chalk for every 700 years.

This shallow ocean was home to a variety of marine animals which are now
extinct. These included giant clams, rudists, crinoids, squid, ammonites,
numerous sharks and bony fish, turtles, plesiosaurs, mosasaurs ,
Pteranodons and even several species of marine birds. Although it seems
unlikelythat you would find dinosaur  fossils in the middle of the Western
Interior Sea, a number of them (mostly hadrasaurs) have been collected from
the Smoky Hill Chalk, and their remains have been well documented. The bodies
of these dinosaurs must have somehow floated hundreds of miles into the seaway before sinking to the bottom. It's possible that they died during a catastrophic flood
and were carried out to sea on a large, tangled mat of trees and other vegetation.

Over a period of about five million of years, the remains of many of these animals
were preserved as fossils in the soft, chalky mud of the sea bottom. When this mud was compressed under thousands of feet overlying shale, it became a layer of chalk that is more than 600 feet thick. Most of the massive chalk formation that once
covered Kansas, however, has been eroded away over the last 60 million years and
is now exposed only in a relatively small area in the northwest corner of the State.
This part of Kansas is now known as the Smoky Hills.

During the last one hundred years or so, the Smoky Hill Chalk has been the source
of thousands of fossil specimens, many of which are on exhibit today in museums around the world.

Some giant clams:
 

Inoceramus grandis - A common, giant  bivalve in the lower Smoky Hill chalk.  (About 18 inches in diameter) How large is this clam shell?

3. Platyceramus platinus: A very large clam shell that occurs throughout the
chalk, sometimes reaching more than four feet in diameter. As the name implies,
these shells are flat and often very thin. While alive, the interior served as shelter
for schools of small fish which are sometimes preserved inside as fossils pressed
into the shell (near the middle of the chalk).

How large is this clam shell fossil?
What is sometimes found preserved as a fossil inside?

Smoky Hill Chalk today:
 

The Smoky Hills change from east to west. The eastern hills are capped with sandstone. This means the top layer of rock is sandstone with other layers, or beds, of rock underneath.  The sandstone was formed from sediment carried by rivers into the shallow seas from the east. Mushroom Rocks, in Ellsworth County in central Kansas, are concretions of Dakota Formation sandstone, originally deposited during the Cretaceous  Period, about 100 million years ago.

 

When the seas dried up in the western part of the Smoky Hills region, thick layers of sediment were left behind. The sediment was later buried between 1,000 and 2,000 feet underground and formed into chalk. Some areas of the chalk bed were later exposed by erosion. Today, much of the chalk at the surface has been eroded away by water. In some areas, tall, steep-sided chalk formations were left standing after

the surrounding chalk eroded away. In Gove County, the Smoky Hill River carved out a large formation called Castle Rock and a series of formations called Monument Rocks. Chalk bluffs also can be found along the Smoky Hill River in Logan, Trego, and Gove counties.

Where would you expect to find the most primitive and oldest fossils?  Would they
be at the lowest layers or at the top layers of sedimentary rock formations.     Why?

Why are most fossils the remains of animals who lived in or near the water?

Look at some pictures of sedimentary structures:   https://www.angelfire.com/nj/PflommScience/sedstruct1.html

Material courtesy of Oceans of Kansas