Just wondering if this could once have been part of a larger trophy:
C.D. Peacock's jewelry store, at State and Adams streets, has an interesting display of the trophies to be given at the American Speed Boat championship second annual water carnival and night pageant, to be held in the basin of Grant Park, August 16 to 24, under the auspices of the Associated Yacht and Power Clubs of America. A huge statue of Neptune and Mercury in silver and bronze, which is said to have cost $5,000, is in the center of the window. Mercury is holding in his outstretched hand a small boat. This trophy is presented by William Wrigley, of Spearmint gum fame. Other trophies are on display presented by William Randolph Hearst, William Hale Thompson. The Hotels Sherman and Brevoort, the Perfecto Cigar Company and George B. Carpenter.
One of the most interesting features of the display is the various knots tied by the apprentices in the U. S. Training Station at Great Lakes, Illinois. Single and double knots, figure eights, knots overhand and Napoleon's bend, are a few of the many difficult examples of the seaman's art in knot tying.
The display next week will be moved to windows at Marshall Field & Company's store, where it will be allowed greater space to show to better advantage the trophies and rope and steel work done by the apprentices. The Neptune and Mercury statue should stand on a huge marble standard, but the latter was so large that it could not be placed in Peacock's window.
Source: Dry Goods Reporter - 26th July 1913
If the original marble plinth was as large and heavy as stated, this may have been the reason why it was parted company with.