Answer:
Rocks which were underwater long time ago.
Explanation:
If we were hunting for trilobites in Canada, we look for those types of rocks where once water present on it because trilobites are the organisms which lived in the marine ecosystem so if they are present in marine so we have to look those rocks which were underwater millions of years ago. Trilobites are the extinct marine arthropods that were present around 521 million years ago.
