Shelling Our Shores

Story by Michelle Brosco Christian. Reprinted from Summer 2006

This large fossil shell found in a cliff deposit at Scientists Cliffs measured in at five inches in width.


Where The Fossils Are

If you want to find the best and most prolific shelling areas, take the advice of an expert—Dr. Peter Vogt, a marine geophysicist who has been walking the beach in Calvert County for over 30 years.
The oldest exposed shell layers in the Calvert Cliffs are near beach level and lie in the northernmost parts of Calvert County, just south of Chesapeake Beach, but shells and fossils are found along the length of Calvert’s eastern coast. Several locations along the Patuxent and Potomac shores are also fossil-rich.
“However, almost all these sites can only be accessed via private land, although according to Maryland law, the beach below high tide is open to the public, and can be reached by boat,” said Vogt.
Shells, sand and fossil sharks’ teeth “tend to work their way southward along the beach, due to the prevailing stronger winds and waves coming from the northeast,” said Vogt. He explained that shells found on the beach “most likely originated somewhere farther north, however, the farther the shells are transported, the more broken and worn they are likely to be.”
The best collecting is usually after a rainstorm, because the supply of shells and other fossils is replenished. In Calvert County’s cliff areas, the fossils are “plentiful in the landslide deposits bordering much of the beach,” said Vogt. However, he warned the danger of landslides is higher after heavy rains. Low tide is a better time than high tide to look for fossils along the beach because more area is exposed. Check the area’s low tide before you go, as some areas have little beach area during high tide. For tide tables, visit www.saltwatertides.com.
 

Razor clams and mussels, pictured, can be found readily.

Humans have long been fascinated with seashells, each one a small work of art. If you’re lucky, you’ll find a beautiful shell—very often a fossil—along numerous Southern Maryland beaches.
A unique geological history is what allows fossil shells to be found along with modern day shells on local beaches, explained Dr. Peter Vogt, a marine geophysicist formerly of the Naval Research Laboratory, and a 30-plus-year resident of Calvert County’s Scientists Cliffs.
“This mixture of fossil and modern shells makes our beaches rather unusual, compared to most of the Atlantic Ocean and other beaches of the world,” said Vogt.
Rivers, including the ancient Potomac, deposited sediments all over Southern Maryland after the sea level dropped and the Miocene sea withdrew, said Vogt. “About 2.7 million years ago, the first big glaciation of North America…caused sea levels to drop, causing our streams to cut deep into their previous valleys, and our current land topography began to form,” he explained.
Within these sediments, large shell beds were deposited in three formations, making local fossil finds anywhere from six to 20 million years old. Some of the sediments are even older, from the Paleocene (55-60 million years old) and outcrop in the northwest corner of Calvert along the Patuxent as well as along the Potomac near the Pope’s Creek area in Charles County, said Vogt.
The prevalence of fossil shells on particular beaches depends upon the area’s past and whether its environment was conducive to creatures that live in shells. What can be found locally are mainly fossil shells, fish bones, sharks’ teeth, ray plates, and occasionally crocodile teeth and turtle bone fragments.

Pictures by Michelle Brosco Christian

“The fact that a good number of fossil shells are not broken before they arrived on the beach by landslide shows that the seafloor environment in which they grew, a shallow embayment of the Atlantic Ocean, was relatively quiet,” said Vogt. “It could not have been a surf zone, otherwise the shells would be much more broken.” The modern shells most frequently found locally are “almost entirely bivalves (except for barnacles) and include oysters, razor clams, soft shell clams and blue mussels,” he estimated.

So just how might one distinguish between the fossil and modern shells? Vogt gives several tips. First, some fossil shells “will have been altered chemically, and changed in color,” he said. Finding two such shells on the beach, he showed that many of the fossil oysters are gray, not white, as they probably once were. “Often times, original colors are gone,” he said.
Another way to determine modern from fossil shells might be from where they are found. Shells found in cliff deposits are all fossils, while shells found on the beach could be either modern or fossil. “It also helps to know that most fossil shells have no close relatives in the modern Chesapeake,” said Vogt.
 

Calvert Marine Museum & Fossil Club

If you’re interested in local fossils, a visit to the paleontology exhibits at the Calvert Marine Museum is a must. The Paleo hall includes a recreated underwater setting depicting Southern Maryland’s ancient sea. Everything from fossil sharks, sea turtles, crocodiles, giant sea birds, whales, dolphins, fossil shellfish, and remains of rare fossil land animals are displayed. A working preparation lab area shows how fossils are conserved and allows visitors to identify their own finds. The museum’s fossil club is open to all. 410- 326-2042; calvertmarinemuseum.com