London, Dec 15 -- A press report, dated today, states: Coast Guard officials said the petroleum-based product that covered most of the city's inner harbour Sunday (Dec 13) was diesel fuel, but they have not determined the source or method of the contamination. Petty Officer 3rd Class Connie Terrell said the Coast Guard boarded barges Monday that had been in the area and took samples for comparison with the diesel fuel taken from the water. "Coast Guard investigators are working closely with the Massachusetts Department of Environmental Protection to identify the source of the spill," said Capt. Raymond Perry, the commanding officer of Coast Guard Sector Southeastern New England. In addition to covering the majority of the city's inner harbour Sunday, the spill extended about 100 yards beyond the hurricane barrier. Terrell said Monday most of the diesel fuel from the spill has dissipated to light sheening through wave action and evaporation. She said there is a thin patch, measuring abo