Residents who have noticed patches of thick tar washing up on the shoreline lately need not fear--it’s not from an oil spill or some other environmental disaster. Affectionately referred to by U.S. Coast Guard officials as “tar patties,” the phenomenon is completely natural, said Timothy Hahn, a coast guard pollution investigator. “Everyone usually gets concerned about it,” he said. “There are a large number of natural seeps in the ocean that let crude oil seep from the ocean floor.” The tar patties can range in size from a half-inch to 3 inches in diameter, he said, and usually wash up on shore after storms. Hahn said the Coast Guard takes samples of the refined oil that comes out of the offshore oil rigs and compares them with the tar patties to ensure the oil on the beach was not the result of a spill.