These marbles were melted by the Great Chicago Fire of 1871 and fused together into this current shape.
These marbles survived the Great Chicago Fire of 1871, one of the worst urban disasters in American history. On the evening of Sunday October 8, 1871, a fire started on the city's Southwest Side, in or near a barn behind the home of Catherine and Patrick O'Leary on DeKoven and Jefferson streets. Eventually, the fire itself burned at an excess of 2,000 degrees Fahrenheit on that night, destroying nearly everything in its path and melting these marbles with the intensity of the heat. Charred relics like these marbles testify the fire's intense heat on that fateful night. Even though the source of the fire remains a mystery, the fire in the end devastated one-fourth of the city, and prompted the nation to aid the disaster-stricken city of Chicago.