A moraine is a mass of stones and earth deposited by melting glacial ice. Many of the large boulders and earth formations in the northern United States remain from the melting GLACIERS of the Glacial Ice Age.
   Moraines are classified according to the pattern in which rocks and earth were left by a glacier. Major types of moraines are the terminal, lateral, medial, and ground.
   Glaciers do not sort the material they carry; the material is of all sizes. The moraine left at the end of the glacier after it melts is called a terminal moraine. It is usually piled up in an irregular ridge, or hill, and marks the farthest point the glacier reached. The unsorted material in a moraine is often called glacial drift or till.
   Lateral moraines consist of earth and rocks heaped along the margins of a glacier. Lateral moraines leave two somewhat parallel lines of material by which the path of a glacier may be traced.
   Medial moraines occur where two valley glaciers came together. The lateral moraines of each join to form a medial (middle) moraine down the center of the new larger glacier, forming the shape of a large Y.
   A ground moraine consists of earth and rock that are deposited beneath a melting glacier.