John Phillips is happiest here, in his favorite classroom. Here, among the trees and on the water, he fuses teaching and the great outdoors into one. One day-long lesson under a boundless sky. One eight-hour journey down one historic river.

This is the Leesburg author and historian's fourth summer leading educational canoe rides on the Potomac River, and today, Phillips nods approvingly at the shallow water and warm air -- ideal conditions for his "Indian Summer on the Potomac" trip.

Ten people took a recent Saturday trip with him, exploring an eight-mile stretch of the Potomac from Point of Rocks to the tip of the Monocacy River.

Les Horn, a Reston physicist, took the same trip more than a year ago and is back with his two teenage sons, Tom and Andrew. Making up the rest of the group were Valerie Weisman and Ed Fleischer of Ashburn, Judy Fincher of Sterling, Laura Larson of Alexandria, Breega Barbree and Russ Martin of Loudoun County, and Breega's sister Catherine Barbree, visiting from Florida.

After a safety lecture, the group broke up into five teams of two. Experienced paddler in the stern, the other in the bow. Shortly after 9 a.m., they set out for the first stop, a small cove on Conoy Island, known on modern maps as Heater's Island.

An hour later, Phillips's students beached their canoes and plopped down on logs for a lecture.

During the 17th century, Phillips explained, tribes from three Native American cultures -- Algonquian, Iroquois and Sioux -- lived in the area. The area the paddlers were about to explore was sort of an Indian no-man's land because it acted as a buffer zone for the three tribes.

During the late 1600s, the Piscataways moved to Conoy Island from their ancestral home in what is now Maryland, partly at the suggestion of the Iroquois, who thought the Piscataways and the Europeans lived too close to each other and were too friendly. Conoy, in Algonquian, means "far, far away."

Phillips and his group then set out for the old Piscataway village on the island. But after more than two decades on Conoy, the Piscataway population was reduced by disease, and a 1722 English treaty setting boundaries for the Native Americans drove even more of them off the island.

The next leg of the trip was shorter, around to the middle of Conoy. An old, abandoned house could be seen through the trees. The walls seemed moments away from falling down, the roof at the point of caving in. The house has been empty for about 50 years, Phillips said. Nearby is a big red barn and rusty remnants of farm equipment abandoned during a flood in the early 1950s.

Farmers had lived on the island since after the Civil War. The Heater family owned the island for most of Conoy's incarnation as an agricultural outlet.

The next stop at Francis Awbrey's landing was quick. The Indians regularly used this point to cross the Potomac, Phillips said, and later, colonists established it as the ferry crossing for people traveling north and south.

The following stop was Noland's Landing, where bald eagles frequent a stand of dense trees.

The ride from Awbrey's to Noland's Landing was long. Arms tired, it was time for lunch and a swim.

"This is where [George] Washington stopped to eat lunch," Phillips told the group.

The ferry crossing began about 1740 and was so important to the Continental Army during the American Revolution that Washington posted an officer there permanently to receive and manage supplies. British troops who surrendered in New York were marched south and crossed here in the winter. And the Marquis de Lafayette, the French general, got reinforcements in 1781 from a Pennsylvania brigade that crossed here.

The crossing was a hotbed of activity, with its own post office, tavern, boot maker and blacksmith. Now it is simply a peaceful place to rest.

Somewhat refreshed, the group paddled on to Phillips's favorite spot on the river -- the fish trap. The river had been unusually still all day, but here, the current accelerated and carried the paddlers along.

Native Americans caught fish by building a stone wall in a V-shape downstream, Phillips said. Fish would be forced to come out of one small spot on the river, where the waiting fishermen would scoop them from the river.

CAPTION: Summer canoe trips on the Potomac River, stopping at historic points and islands, are popular. Ten area residents, including Les Horn of Reston, at left, and Breega Barbree of Loudoun County, recently made an eight-mile trip on the river west of Frederick. Horn and Barbree are examining arrowheads on Conoy Island.