According to an ancient Wampanoag legend (or a recent Chamber of Commerce ad campaign, take your pick) Nantucket's origins lie in a pair of ill-fitting slippers worn by a giant named Maushope. Apparently Maushope liked to use Martha's Vineyard for a La-Z-Boy, kicking back and taking long pulls off his favorite pipe. The dense fog that often wreaths the islands is still referred to as "Maushope's smoke"; by tour guides and airline ticket agents nervously trying to explain why there are no planes flying that day.

Anyway, one day old Maushope was trying to relax after a long day of whale-flinging (another tale in itself) but something just wasn't right: he had a pebble in his moccasin. Now we can all identify with how irritating that can be, but it was made far worse by the fact that the "pebble" was roughly the size of a house. Maushope did what any of us would do with our shoe in that situation: he chucked it. Rather far, actually. The moccasin became the island of Nantucket, and presumably Maushope walked around with one heavily callused foot from then on.

I have a theory about this story: it's true. Well, maybe not the part about the pipe smoking, but I wonder if this and other legends about Maushope aren't some vestigial group memory of a time long ago, when the land was very different. I wonder if perhaps ole Maushope wasn't a glacier.

There seem to be two group of stories about Maushope, one in which he is a great leader of his people, and the other in which he is a fairly solitary individual who is responsible for the world around us. Maybe there really was a great chief or sachem named Maushope who was revered by his tribe, and as his legend grew he was credited with greater and greater feats, including creating the Cape and islands. Many of the latter stories involve stones, or scraping, and the engagement of titanic forces by a relatively quiescent giant. Again the pokeweed habit poses a bit of a problem but that's the exception that proves the rule.

Whether or not Maushope was in fact a glacier may be problematic, but the evidence that remains of his ancient temper tantrum can be seen to this day, once you know what to look for. A leisurely tour of Nantucket reveals hidden secrets of history that lie in plain view. For this journey it would be helpful to have a map of Nantucket handy, readily available at the Visitor Services office; your exploration will be greatly enhanced with visual aids.

Standing on Steamboat Wharf and facing east toward the Upper Harbor, one is presented with a study in contrasts: to the left are the low-lying sandy pennisulae known as Coatue and Great Point (called Nauma by the Wampanoags); to the right is a long range of undulating hills that begins at Wauwinet in the east and swings around to the north near town, encompassing Quanaty Bank (the hill under Orange Street), the Cliff and the north shore of Nantucket. These two broad groupings have completely different origins, ones that lie far apart in time and method.

Coatue and Great Point are barrier beaches that are relatively recent in geological terms, formed initially around six thousand years ago by the action of wind, waves and tides. The sand that they are made of, indeed, most of the sand on Nantucket, is the finely ground evidence of unbelievably ancient and powerful forces. Composed primarily of feldspar, garnet, magnetite and especially quartz, these tiny grains originated far to the north as part of the mountains of Vermont and New Hampshire, where they were gouged out of the living rock by the enormous glacier that then covered most of North America.

These numberless grains of sand that form our barrier beaches are in a constant state of flux, moving restlessly along the shoreline. The currents that direct them sweep the particles northward, in the case of Great Point, and east-west on Coatue. The jetties that you see when you first arrive at Nantucket on the boat were built to halt, or at least slow, the relentless march of the Coatue barrier beach. It was exactly this process that contributed to the decline of the whaling industry: when there were no jetties a sandbar eventually formed across the opening to the harbor, blocking larger ships from off-loading their cargo of whale oil. By the time that the jetties were built, the few whaling ships that were left had already moved on to ports with deep-water access.

There are examples elsewhere on the island where this process has reached its natural conclusion: Sesachacha and Capaum Ponds were both originally open to the sea and eventually cut off by a barrier beach. Part of the reason for the removal of the town of Sherburne from its original location (mid-island around the Sandford Farm to Crooked Lane) to where the downtown is today was that the old harbor -- today's Capaum Pond -- was closed off during a storm.

The environment of a barrier beach is fairly harsh, and it takes a particularly hardy plant to make a go of it there. Coatue in particular plays host to an interesting range of plants, from the prickly pear cactus (at the northern extent of its range) to reindeer moss, a pale green lichen that was brought to Nantucket by the very same glaciers that created the sand that it grows on. At the time of the last ice age, the area around Nantucket was a series of low-lying hills on a chilly, windswept tundra populated by caribou that feasted on the reindeer moss; though the ice and the caribou are gone the moss has persisted here ever since. There are also cedar trees to be found on Coatue as well though they are far smaller than their mainland cousins, hunkered down to avoid the nearly constant attack of wind and salt spray.

The next leg of our journey takes us to the eastern end of the island, specifically along Polpis Road. Anyone who has biked that route out to 'Sconset will tell you -- breathlessly -- that it is a whole lot hillier than the Milestone Road. Polpis Road runs along the ridge of elevated land that I mentioned earlier; its origin lies much further back in time than the barrier beaches that we just left. As you are traveling along the Polpis Road you are roughly following the terminal moraine of the ancient glacier that formed the nucleus of or current island.

Stop and think about that for a moment (well, don't actually stop -- you might be rear-ended by someone, and I can't afford another lawsuit); fifteen thousand years ago, right on this very spot, was a mile-high wall of ice that reached from here all the way to the North Pole. We've all seen pictures of glaciers in mountain valleys: dirty, jagged rivers of ice slashed through here and there by torrents of melting run-off. Now expand that image to include much of the Northern Hemisphere.

This range of hills that you are traversing, from Pocomo Head and Saul's Hills in the east through downtown and Popsquatchet Hills at Dead Horse Valley to Trott's Hills in the west, actually overlays an incredibly ancient ridge of bedrock. Millions, not thousands, of years ago there was a mountain range on that very spot that roughly followed the same line. As eons passed, the mountains were worn down by the inexorable action of wind, water and time, leaving little more than nubs of rock as a memorial to the former mountain grandeur. These nubs and their accumulated debris caught Maushope's foot and held it fast.

Twelve thousand years ago, assaulted by warm air and currents flowing from the south, the glacial ice disgorged the detritus that it had picked up during its journey, everything from tiny bits of soil to boulders as large as houses. Heavier objects were not carried as far as the lighter particles of sand and soil, so as a result Nantucket has very few large boulders -- called erratics -- but plenty of beautiful fine-grained sand. Most of the larger stones that are "native" to the island are found in this range of hills; you can see many for yourself if you make a short side-trip to Altar Rock.

To get there you need to find the Red Gate (the former entrance to the old Town Pasture) -- it will be on your left about half-way along the Polpis Road. Right across the street from the gate is a dirt road; if you follow that, passing a building that looks like a giant bottle of nasal spray, you will eventually arrive at Altar Rock itself. From the vantage point of that hill you will be able to spot a number of glacial erratics, including a few larger ones that remain as mute testimony to the awesome forces that brought them here from their homes far to the north.

Altar Rock is also a great spot to get a sense of the different types of glacial landforms to be found on the island. To the north, east and west are the low, undulating hills where Maushope's mile-high foot lay; you might even catch a glint of water in the valleys between them. Those are called kettlehole ponds, and they too are reminders of Nantucket's icy past. As the glacier receded it left behind enormous chunks of ice that calved off from the larger mass, remaining awkwardly behind like that dinner guest who just doesn't know that it's time to leave. The mass of ice formed a depression in the thawing ground that reached all the way to the water table; eventually the ice melted away completely, but the hole it had created remained, filled with water.

There are a number of such kettlehole ponds across the island: Gibbs Pond, Almanac Pond, the Pout Ponds, No Bottom, Maxcy and North Head of Hummock ponds are all the ancient resting places of stranded icebergs. Since they have no streams feeding them their level rises and falls with the water table. These ponds are also prone to being filled in by successive layers of decaying plants and sphagnum moss, eventually becoming bogs. Waqutuquaib Ponds, located just off Madaket Road and adjacent to Sanford Farm, provide an excellent example of this process in all its slow-motion glory.

Anyway, back to Altar Rock. The view south is of a long, flat expanse, reaching from 'Sconset to Madaket, that terminates at our sugar-sand beaches. This is the outwash plain of the glacier, essentially a kind of delta consisting of the accumulated smaller debris left behind by glacial runoff. You have probably already experienced the thrill of the outwash plain if you've made the trip to 'Sconset. Chances are you took the Milestone Road, that long, straight rather boring bit of tarmac that bisects the island; its path traces the beginning of the plain proper. If you are coming from Altar Rock, a good way to get a sense of the transition is to continue east on Polpis Road, following it along Sesachacha Pond (with its barrier beach) past Sankaty Head (more terminal moraine) to 'Sconset itself. Grab an ice cream or soda at the market -- you'll need it to stay awake for the trip back along Milestone Road.

You might try staying alert by imagining what the place used to be like: twelve thousand years ago, from the melting edge of the glacier, a flat featureless plain, intersected by ice-cold torrents of muddy water, stretched out for over forty miles before ending at the sea. Caribou, elk and mammoth ranged over the frozen, windswept tundra that lay at Maushope's feet. If there is evidence of a human presence in the area it is probably at the bottom of many fathoms of water; in all likelihood humans clung to the more temperate shoreline, where food was plentiful and less prone to trampling the odd hunter.

I'm exaggerating a bit when I say that the outwash plain is totally flat -- you've probably noticed that the land undulates slightly, and is interspersed with long valleys that run north-south to the ocean. They are the nothing less than the eroded remnants of ancient riverbeds, formed by the melting runoff from the glacier. Some of these, like Maddequecham, are dry; others, however, are filled by ponds, and retain vestigial memories of their ancient riverine origins.

Weweeder, Miacomet, Hummock and Long ponds all have a distinctive elongated shape that is very different from the more typically roundish kettleholes. Like kettlehole ponds they are either fed by springs or lie below the level of the water table, but their very different origin is obvious after even a cursory glance at a map, once you know what you're looking at. It's not all that hard to imagine them in their earliest form, engorged with the icy, dirty meltwater flowing from glacier just to the north.

There exists yet another reminder of the origin of these ponds as rivers: to this day herring (alewife) and white perch return to these ponds to spawn. Known as anadromous fish, they live much of their lives in salt water but return to fresh water to spawn, often to the very same place where they themselves were hatched. Each spring this antediluvian ritual repeats itself, as it has done for thousands and thousands of years. These days however the fish need a helping hand from humans; the openings where these ponds meet the sea are quickly closed by barrier beaches, and must be opened mechanically each season to allow the process to continue.

You can really get a sense of how different these long, narrow ponds are from their kettlehole neighbors if you extend your tour of the island to include a trip to Madaket. While Madaket Road has many more twists and turns than the Milestone Road, most of its length duplicates the long, gentle valleys of the latter. First bridge, which features a lovely picturesque view of our local landfill, crosses the divide between North Head of Long Pond and Long Pond proper. As you stand on the wee pier that juts out into the pond, try to imagine the limitless expanse of tundra before you, slashed through with swollen, muddy rivers of icy runoff. A frigid, biting wind cuts through your bearskin and chills you as stand there wondering when someone is going to get around to inventing Gore-Tex.

A final brief tour of Madaket reveal two more prominent barrier beaches: Smith's Point and Eel Point, which are roughly as old as Coatue and Great Point. Of course in a way measuring the age of such a transitory feature is pointless; for instance, what is Smith's Point now is very different from when it Esther's Island not too long ago, or when it was a long barrier beach known as Nopque that stretched all the way out past Tuckernuck Island. No doubt next year it will change yet again, shaped by the same forces of wind, water and time that have long sculpted our island home.

Knowing about the geological history of Nantucket adds another dimension to our appreciation of the island. It helps us to understand how the human history of the Grey Lady has been influenced by the very fabric of the island itself, how the poor soil and limited natural resources turned the early settlers away from farming and industry and toward the lure of whaling. It also places us within a vastly larger context of time, one that allows us to glimpse the titanic, inexorable forces that have wrought dramatic changes on the land, and puts our puny human efforts into perspective. Though we might think that we hold dominion over the land, sea and air, and all that live there, ultimately we are all merely squatting in the time-worn remnants of Maushope's moccasin.