Out of an existing stream, Montayne's Rivulet, they created alternating bodies of still and rushing waters that begin with the large, triangular Pool just inside Central Park West at 101st Street. The present project has not affected the Pool, but a first-time visitor will still gasp at the romantic vista of flat water brushed by weeping willows.

The Pool empties eastward over the Cascade, a 12-foot-high drop of boulder-steps. These were painstakingly assembled by Frederick Law Olmsted and Calvert Vaux, the park's designers. But by 1980, when the nonprofit Central Park Conservancy was established, erosion and vandalism had reduced them to a jumbled heap. Using old photographs from the collection of Herbert Mitchell, the former rare-book librarian at Columbia's Avery Library, the conservancy repositioned the rocks into the original scheme.

The Cascade plummets into a still, slow-moving channel at the bottom of a ravine, with rocky, soil-studded slopes on each side. It then flows on under Glen Span Arch, a giant rough stone bridge that carries the west vehicular drive overhead. Then the watercourse meanders forward into a shady oval unnamed in early Central Park maps except by inference -- the glen.

In this area, subsurface drainage has been restored, topsoil has been stabilized and what had been a mud flat has been dredged of up to five feet of silt, restoring its original character as an irregular canal about five feet wide and perhaps 150 feet long. This empties under another rustic bridge where it proceeds on into the Loch, now a swamp of neglect.

This stretch, from the Cascade on down, is a masterpiece of landscape manipulation. As visitors follow the streamside path, they see the noisy, sunny brightness of the Cascade disappear into the silent, tomb-like darkness inside the massive arch.