The most spectacular glacial erratic in the Bronx River valley is the Rocking Stone in the Bronx Zoo.Ten feet wide, over seven feet high and weighing some 30 tons, the pink granite boulder was carried down by the glaciers of the last Ice Age.>When the glacier finally melted, it left the huge stone perched atop a bedrock outcrop overlooking the newly-carved course of the Bronx River.
The bedrock displays grooves worn by the friction of stones pushed across it by the glacier, including the groove made by the Rocking Stone itself as it was eased towards its final resting place.Once there the stone was left so finely balanced that the force of one or two men could make it visibly rock on its natural pivot.Rocked, but not moved: local legend tells of a team of 24 oxen that once tried and failed to dislodge it.
Colonial surveyors used the stone as a landmark to fix the northern boundary of the town of West Farms, and the DeLancey family, who once owned the land thereabouts, would often take their weekend guests for a carriage ride from their mansion just across the Bronx River to see the wonderful Rocking Stone.
When the Rocking Stone was included in the new Bronx Zoological Park in 1895 it quickly became one of the zoo’s most popular attractions, depicted on postcards and innumerable family photographs showing people putting their shoulders into it.Zoo officials, though, feared that one day someone was going to rock the Rocking Stone a bit too far, and so they shored up its base.Today the Rocking Stone rocks no more, but you can still see it right outside the House of Darkness.You can also look at the glacial grooves in the bedrock and feel them with your fingers, a most accessible piece of the geological history of the Bronx River.
Stephen Paul DeVillo