Giving up on fishing for the moment, the group decided to explore. A collector of sharks' teeth, Hill knew the area was rich in fossils.

What Hill didn't know is that he and his friends were in a dangerous area where digging for such treasures was forbidden, except by trained experts. And he didn't know that an amateur fossil hunter had died in a cliff collapse in the area five years earlier; there were signs on parts of the property warning would-be explorers of the dangers of climbing on the cliffs.

So when Hill found a bone sticking out of a cliff, the group immediately began digging. Two hours later, they had unearthed 12 bones.

The word cetothere wasn't even in the vocabulary of Hill, Gordon Showalter, Wayne Sizemore, Joyce Young and Fritz Vesey when they set out on the fishing expedition from Hill's Cobb Island, Md., cottage. Now they know it is a 35-foot extinct whale from the Miocene Epoch. And they also know that the cetothere bones they found are 15 million years old.

The bones -- fragments of the flipper of the extinct whale -- are now resting safely in plaster on a shelf at the Smithsonian, waiting for closer examination.

"We were walking along the beach at what I then thought was Westmoreland State Park and I saw a piece of bone about three inches long sticking out of one of the cliffs," said Hill recently about his mid-August experience. "It was about head level, and I immediately called my other friends from the boat."

Using their hands and a screwdriver, and pouring water over the area, Hill and his companions carved out a chunk of bone that was shaped like an axe handle. "We were all really excited," said Hill. "I had had an excavation course in high school and I knew not to grab it and pull it out. I knew it must have been hundreds of thousands of years old."

After carefully digging the bones out of the cliff, the group laid them in two beer cartons on the boat. A few days later, Hill brought them to the Naturalist Center at the Smithsonian's Museum of Natural History.

Hill, 20, a Woodbridge resident who attends Mary Washington College in Fredericksburg, recently revisited the site with paleontologist Frank Whitmore.

Whitmore, a geologist with the U.S. Geological Survey and a research associate at the Smithsonian, said Hill's find is "a significant research contribution to paleontology," the study of prehistoric life through fossils. Whitmore said the bones will be "very valuable" in his research on cetotheres, since a fossil find of this sort occurs only about once a year in this area -- one of five locations in the world where cetothere fossils have been found.

Clayton Ray, a curator at the Smithsonian's department of paleobiology, said the location where the bones were found is "a very rich area in which we have been accumulating fossils for many years, such as sharks, turtles, porpoises, whales and crocodiles." New finds in the area are made when erosion exposes new areas of the cliffs, he explained.

The reason that cetothere fossils have been preserved comparatively well in this area, according to Whitmore, is because they are lodged in clay rather than sand. "Clay does not let the water flow through it constantly like sand does," said Whitmore. "This helps in preserving the bones."

The cetothere was common to this part of the country 15 million years ago, when the climate here was similar to that of northern Florida and creatures such as rhinoceros, three-toed horses, tapirs, mastodons and camels roamed the land.

"The areas of Chesapeake Bay and Northern Virginia rivers and North Carolina are all noted for fossil marine mammals," said Whitmore, who depends heavily on amateur collectors such as Hill to inform him of fossils they've spotted. "They are rare enough that if I spent all my time looking for them, I would get very little else done," he said.

Whitmore arranged to meet Hill and investigate further in the spot where the bones had been found. The cliff turned out to be on the property of Stratford Hall, the birthplace of Robert E. Lee, now a working plantation and park run by a nonprofit organization with strict rules about digging on its cliffs.

Whitmore, who has worked frequently with officials at Stratford Hall, was given permission to excavate. His further diggings turned up 16 consecutive vertebrae of the cetothere as well as ear bones, which were added to the flipper fragments brought in by Hill.

Although happy about Hill's find, Whitmore said sporadic digging by fossil hunters along the rivers and the bay has become a major problem. "No one should ever dig without finding out who owns the property and getting permission," he said. "How would you like it if somebody came into your front yard and dug a hole there?"

Officials of Stratford Hall, where an amateur fossil hunter died in a cliff collapse five years ago, will allow only experts to go near the cliffs, and then only after signing a release.

"We absolutely do not permit any digging in the cliffs that is not supervised," said Stratford Hall Executive Director Admiral Thomas E. Bass. "Amateurs can have tragic acccidents there because cliffs are subject to landslides at any given moment." Bass said the facility does allow visitors to walk the two-and-a-half miles of beaches on the 1,600-acre site to look for sharks' teeth, as long as they do not approach the cliffs.

At neighboring Westmoreland State Park, Whitmore advises amateurs that, although they can look for sharks' teeth on the shores, it is against Virginia state law to do any excavating in a state park without permission of the State Park Board in Richmond.

Inexperienced fossil hunters should be concerned for their own safety as well as the safety of the fragile bones they find, said Whitmore. As a rule his advice is to leave digging to the experts. "The common error made by amateurs is that they keep pecking away at the bones and they break them up," he said.

Due to the backlog and small staff, it may be years before Hill's fossils are cleaned and examined.

Meanwhile, the strange-looking paperweights on Whitmore's desk -- cetothere's ear bones -- are drying off in preparation for closer examination. The other bones remain in storage at the Smithsonian.