About 400 million years ago, a small, narrow continent collided with proto-North America. The heat from the pressure melted the quartzite, which allowed it to bend the quartz pebbles and Silurian Shawangunk Conglomerate. This layer was then uplifted and cracked over thousands of years. During this period, the Delaware River slowly cut its path down through the shattered and cracked quartzite. If the quartzite had not been cracked, the river would not have been able to cut its path through the mountain to form the gap.