About 22,000 years ago, a glacier crept up and covered the northern half of Long Island. The glacier stopped there for a while. The melting edge dropped rock pieces in a long pile, called a terminal moraine, in the middle of Long Island. The glacier backed up and stopped again, about 20,000 years ago, along the north shore. It piled up some rocks and sand, creating a recessional moraine.
Ground moraines are pieces of rock the glaciers drop as they travel.
A stack of those pieces created Port Washington peninsula. Streams of melted ice flowed in front of the glacier, carrying sand, gravel, silt, and clay. They also created flatlands. The land there tends to be fertile because of the silt. The southern half of the island is very different from the northern half because the plains are flat and sandy on one half and there are jagged rocks on the other.