Shark's Tooth Island (also known on the maps as Hollis Marsh) is a privately owned island in the Potomac river.  It forms the boundary between the Potomac, Nomini Bay, and Currioman Bay.  The island is basically a long narrow sand bar that is formed from the sand (and fossils) washing down the river.  The entire area is part of an 18M YO inland sea.  Most of the fossils wash down from the three tall clay cliff areas:  Stratford Hall, Westmoreland State Park, and Nomini Cliffs.

If you do go looking, the middle part of the island (islands depending on the tide) is one of the best places to go:  you will find numerous shark's teeth on both sides of the sand beach.  The average size will be about 1/2" or maybe slightly smaller but occasionally we will find ones as long as 2".  I average finding a tooth or fossil about every 50 seconds.  Yes, you read that correctly.  The southern edge of the island is a very popular area for weekend boaters.  (You will see the volleyball net on that end.)  I can find small teeth in nearly every handful of sand I pick up (slight exaggeration), but almost all of these are very small.  The northern edge has some good teeth, but the quantity is far smaller, so the middle is usually your best bet.  I took seven kids all under 10 to the middle and they found a combined 200+ teeth and bones in less than 2 hours.

In addition to shark's teeth you will find numerous small bones and ray dental plates.  The best fossil we have found is probably a complete whale vertebra measuring about 8" in length.  The bones are lighter than the rocks so look higher up the banks, especially in the reeds where they wash up and lodge.

As for the cliffs...  the Nomini cliffs across from Shark's Tooth Island feature a number of very good teeth.  I saw a huge tooth there the other day, but the quantity is relatively poor and the granite rip-rap that has fallen makes it harder to find things.  All of the cliffs are relatively high (up to 150') and there is definitely a danger of a slide especially after a storm which is, after all, the best time to go looking for new fossils.  The other danger is that the clay holding the fossils can extend all the way into the water so it can be extremely slick and easy to slip and hit your head on a big rock.  I've seen big bones (and a few teeth) sticking out of the clay.  Westmoreland State Park is probably the best place to go if you want to dig in the clay.  Actually finding the property owners can be tough on some of the other locations.

Shark's Tooth Island is privately-owned and runs sort of like a camping club.  2008 dues were $125 I think (not $300) and that lets you go for an entire year and takes some number of guests.  If I understand correctly, the family that owns it mostly collects the money to stabilize the island and pay the real estate taxes.

BTW, the same Miocene era fossils can be found on a similar cliff formation on the Rappahanock river at the Horsehead Cliffs north of Tappahanock.  We found a beautiful 4" shark's tooth there, but haven't ever found any bones.  I am told that Calvert Cliffs on the western side of the Chesapeake Bay is similar to these two other areas.

Happy hunting.