Quoted from Museum of American Financial History:
"Just before noon on Wednesday, September 16, 1920, a horse-drawn wagon covered with a canvas tarpaulin pulled to a stop on the north side of Wall Street across from the House of Morgan. The driver abandoned the wagon and blended in with the lunchtime crowd before the dynamite-packed wagon exploded. Debris ricocheted through the canyons of the Financial District and shattered windows as far as half a mile away. The bombing was likely an attempt to steal the $900 million worth of gold ingots being transferred that day. If that was the intent, however, the heist was unsuccessful, as no gold was stolen.
"The attack killed 38 people and injured more than 300. Junius Morgan, grandson of company founder J. Pierpont Morgan, suffered only minor injuries to his hand. J.P. "Jack" Morgan, Jr., then president of the bank, was traveling in Scotland at the time of the attack. When he returned, he found his building pock-marked from the explosion. These marks can still be seen on the facade of the Morgan building today.
"Both the House of Morgan and the New York Stock Exchange, located across the street, closed that day but reopened for business the following day. When trading resumed, stock prices moved upward. At the time of the attack, more than 3 million people worked in the factories, warehouses, department stores, specialty shops, and skyscrapers on Wall Street, where one-third of New York City's workforce was employed in white collar jobs. Bolshevik groups and anarchists were accused of the bombing of the Morgan Bank, but no one was ever brought to trial."
You can find pictures of the pockmarked wall and a more detailed description of the events of the day at Wall Street: Beyond the Wall: Terrorism.