Travel Reference
In-Depth Information
As we resume our stroll along the ancient sedimentary beds that now
make up the Sucia Island shore—and thus move ahead in time—we begin to
see marked changes in the fossil evidence. We are now well into the sand-
stone beds. The fossils here are still fragmented, but now there are far more
of them than below, in the conglomerates, and here in the sandstone they
ate concentrated in distinct beds. These beds are packed with the remains of
small snail and clam shells. The clam fossils look a lot like clams found in
today's shallow seas. The layers they sit in look much like sedimentary beds
sculpted today during large storms, and we can assume that these ancient
beds were formed in similar fashion, during large storms striking the ancient
seashore that was Sucia Island, more than 75 million years ago.
As we continue our trek, we observe that the coarse sandstone begins to
change subtly in appearance. There are fewer of the shell layers and more fos-
sils occurring singly or in small groups. The fossils appear better preserved as
well, and some are much larger than any we have seen before. The majority of
fossils are clam shells, but there are many snails as well. Two types of fossils ate
most noticeable because of their large size and abundance: long prism-shaped
clams, some half a foot long, and other clams with a very knobby and sharp-
ridged appearance. The first of these is a clam known as
Pinna,
which can be
found in abundance today in many tropical regions of the world. The second
is
Trigonia,
found today only in Australia. The presence of these two fossils is
another type of clue: It alerts us to the possibility that the ancient Sucia envi-
ronment was far more tropical than now, that these fossil lived in shallow seas
of the type we find in the coral reef latitudes. When we examine the snail
shells hete on Sucia, we arrive at a similat conclusion. Most of them are made
up of species that today are found only in shallow, warm, tropical seas.
Now we move faster through time, ever upward through this pile of
stacked strata, and the sand gives way to a finer sediment. All vestiges of the
shallows begin to disappear: No longer can we see any evidence of storm
beds, no longer can we see the ripples that waves might fotge. It is as if we are
standing at the bottom of an aquarium that is slowly being filled, and the
level of the sea rises above our heads.
