West 114th Street between Riverside Drive and Broadway is a quiet sloping block of light brick rowhouses, similar to other side streets in the area.

But there's one massive difference that sets West 114th apart: the 100-foot rock lodged between two houses and walled off behind an iron fence.

This hulk of Manhattan schist was nicknamed Rat Rock years ago by locals, who were understandably spooked by the rodents that used to enjoy nesting there, according to a 2000 New York Times article.

Like all the rock outcroppings found in Manhattan, the story of Rat Rock began hundreds of millions of years ago, when the bedrock that helps support skyscrapers was formed. Manhattan schist is a type of bedrock, and while most bedrock lurks beneath ground, geological fault lines forced some rocks to the surface, The Times piece explains.

Having big boulders above ground wasn't a problem in Central Park. Though some were dynamited away when the park was being built, others were left behind to provide a rustic feel amid the lake, pond, and pastures.

Rat Rock in 1917

But when developers encountered rocks like this on the street grid, they either blasted them away or left them alone. For unknown reasons—perhaps because it's just so enormous—Rat Rock remained, and builders worked around this break in the streetscape.

Apparently, it's here to stay. The land is owned by Columbia University, and they have no plans to get rid of it. "The lot and development rights are incredibly valuable, but removing the rock could cost hundreds of thousands of dollars," states The Times.

Enormous boulders like this didn't get in the way of nearby development a century or so ago, however. The Museum of the City of New York has this 1903 photo in its collection of a similar rock thwarting the building plans of a row of houses on Riverside Drive between 93rd and 94th Streets.

I'm not so sure this photo is labeled correctly; it doesn't look like the Riverside Drive of the era to me. But assuming it is, the rock has long been removed.

Over on the East Side, this undated photo shows rock outcroppings at Fifth Avenue and 117th Street, with modest houses built on top of them far off in the distance. The rocks here are no longer.

Riverside Drive is one of New York's most historic (and beautiful!) streets. Join Ephemeral New York on a walking tour of the Drive from 83rd to 107th Streets on October 24 that takes a look at the mansions and monuments of this legendary thoroughfare.

[Third image: New-York Historical Society; fourth image: MCNY x2010.11.3102; Fifth image: MCNY 93.91.367]