Your first paragraph ...Hollis Marsh or Hollis Island, nicknamed Sharks Tooth Island is a great little area to anchor your boat or park your kayak and scan the shoreline for fossilized shark and porpoise teeth, shells and vertebrae and stingray dental plates from creatures that inhabited this area many, many years ago.
Permit-holders can scour the sandy and marshy areas for Miocene Epoch fossils which are millions of years old! The teeth of extinct sharks most commonly found here belong to the Tiger, Requiem, Mackerel, Hammerhead and the Sand Shark. Teeth of the spectacular giant White Shark, (Carcharondon Megalodon) are found here too, but are rare.
The smaller-sized teeth are plentiful on Sharks Tooth Island and it's possible to find larger ones as well. The teeth in the photo above were all found within about a 20-minute timeframe.
Here are printable fossil identification sheets in PDF format to help you identify the sharks teeth as well as the shells that can be found in the area. You can try and match the teeth in the photo above to the ones on the sheet to see which species the teeth are from.
Watch out for jellyfish if you visit the area. Don't get stung! Bring some vinegar to apply to any jellyfish stings just in case.
The island is privately owned. Here's the contact information so you can secure a permit to visit. Hollis Island Owners, c/o Melvin Foxwell, 751 Bushfield Road, Montross, VA. 22520. Phone 804-472-3416