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The object’s composition and provenance remain unknown almost two weeks after first contact because, in a state-of-the-art tunneling machine, as it turns out, you can’t exactly poke your head out the window and look.

“What we’re focusing on now is creating conditions that will allow us to enter the chamber behind the cutter head and see what the situation is,” Chris Dixon, the project manager at Seattle Tunnel Partners, the construction contractor, said in an interview this week. Dixon said he felt fairly confident that the blockage will turn out to be nothing more or less romantic than a giant boulder, perhaps left over from the Ice Age glaciers that scoured and crushed this corner of the continent 17,000 years ago.

But the unknown is a tantalizing subject. Some residents said they believe, or want to believe, that a piece of old Seattle, buried in the pell-mell rush of city-building in the 1800s, when a mucky waterfront wetland was filled in to make room for commerce, could be Bertha’s big trouble. That theory is bolstered by the fact that the blocked tunnel section is also in the shallowest portion of the route, with the top of the machine only around 45 feet below street grade.

“I’m going to believe it’s a piece of Seattle history until proven otherwise,” said Ann Ferguson, the curator of the Seattle Collection at the Seattle Public Library, who said she held out hope for something of 1890s Klondike Gold Rush vintage, when Seattle became the crazed and booming gateway city to the gold fields of Alaska and Canada.