As the massive ice sheet retreated north to Canada, streams flowing from the melting water formed chains of lakes. Water dammed by glacial moraines, low ridges of rock and soil left behind by the ice, created additional pools. This and other geologic action left Maine specked with 5,700 lakes and ponds and bisected by hundreds of streams and rivers.

In time, aspen, spruce and birch trees emerged along these new shorelines, as Maine's tundra-like landscape progressed to forest.

By 5,000 years ago, prehistoric people had learned how to use raw materials from the evolving forest to build boats that were strong but light enough to carry between lakes or around rapids. The Penobscot Indians called their canoes ''agwiden,'' which means ''floats lightly.''

In his book, ''Above the Gravel Bar: The Indian Canoe Routes of Maine,'' historian David Cook of Winthrop writes that the development of the birch-bark canoe was a revolution for native people. It was the equivalent of inventing the wheel.

''The wheel had absolutely no application in a region of unbroken forests,'' Cook writes. ''The people of the Maine and Canadian woods didn't need the wheel, for they had something far better; they had the birch-bark canoe.''

Ranging from 14 feet to 21 feet long, birch-bark canoes were made by turning long sheets of bark inside out. The bark was fitted onto a hull constructed of cedar and held together by roots of the spruce tree. The bark was made watertight by a boiled mix of spruce resin, charcoal and fat.

A 15-foot birch-bark canoe weighed roughly 60 pounds, not much heavier than modern canoes made of aluminum or plastic. The light weight made it possible for hunters to pole upstream in search of game or to carry their canoes into watersheds that led to distant rivers.

The glacier left Maine's earliest residents with a highway system. The birch-bark canoe gave them a means to get around.

Glaciers and the ice age

The University of Vermont has a site about glaciers and the glacial ages. It answers what glaciers are, what their effects are, how often ice ages occur, and when we can expect the next one.

Canoeing and birch bark canoes

"Arnold Invades Quebec: Canoe-borne attack follows Kennebec, Dead and Chaudiere" is about Colonel Benedict Arnold's birchbark-canoe invasion of Canada, the first amphibious military assault in our nation's history.

Margaret's Algonquin Park Page has tips for planning a canoe trip.

Canoe and Kayak magazine online

The Paddlers' Web

Chat about paddling in the GORP Paddling Forum

Maine Sportsmen's Guide to river trips

Checklist for canoe campers

Top ten tips for safe canoeing