Scientists are stepping up efforts to identify a mysterious gooey substance polluting waters along the eastern edge of San Francisco Bay, coating hundreds of sea birds and killing scores of them, a state wildlife official said Tuesday. Initial field testing of the slime, first reported on Friday, came back negative for petroleum but authorities hope a more comprehensive laboratory analysis will provide some conclusive results, said Andrew Hughan, spokesman for the California Department of Fish & Wildlife. More than 100 birds, mostly ocean-going water fowl, have died after their feathers became soaked in the colorless, odorless goop, impairing their ability...