These are great for fossil-hunting with kids. Trilobites are found in sedimentary rock - the kind which flakes off in layers. Why so common? When Trilobites gathered in large numbers under/near a slope and that slope collapsed, they were trapped. Their remains were fossilized. Where you find one there will be many.
The most well-known place in Newfoundland is at Manuel's River on the Avalon Peninsula. I explored an area on Random Island, at the base of Trinity Bay and near Clarenville. There, on a hillside, was sedimentary rock and an occasional Trilobite. You have to pick through many pieces of loose rock to find one. It's amazing that the entire area was once under water.
Here's one of mine below.
T.