In 2004 I wrote an article for the Boston Globe about some wagon tracks and hoof prints that had appeared in the surf after a severe storm on Cape Cod. The tracks looked like they had been laid down the day before, but they had actually been made 300 years ago. Then, Cape Codders used horses and oxen to cut salt marsh hay and ship it to what we now call Hay Market Square in Boston.
The tracks also showed that the beach had migrated 800 feet inland in the intervening 300 years because the sea has risen over three feet since the 1700s.
So when natural history photographer Sandy Tilton sent me photographs of fossilized hoof prints she had taken on Salisbury Beach, I figured I had about the same thing.
The biggest difference between the two sites was that the Salisbury hoof prints had been made in clay while the Cape Cod tracks had been made in peat. So the Salisbury prints were a lot more distinct than those on the Cape. Plus there were no tracks left by hay wagons in Salisbury so this had not been where people had been cutting hay.
Our second thought was that the site might have been a hard spot on the marsh where farmers kept their horses during the haying season. But that didn’t explain the other artifacts on the site.
The clay was about a foot thick and stretched along the beach for almost a quarter of a mile. Most of the hoof prints were concentrated in the center of the site but there were also hoof prints and even human footprints concentrated in small areas throughout the site. Then there were ancient scratches in the clay that looked a little like the markings in Nazca, Peru, that only make sense when you fly over them in a plane.
There were also pieces of metal and wood scattered throughout the site but the most perplexing artifact of all was a set of small, deep-seated parallel tracks that ran in a long straight line.
We tossed around several theories for what had gone on at this site. Perhaps it was the location of a small farm or even where colonists had salvaged a wreck, but these explanations also had flaws.
The clay was our biggest dilemma. Victor mentioned it had probably lined the bottom of an ancient pond. That night it hit me. You often find stretches of wild cranberries in clay-bottomed swales behind the dunes in places like nearby Plum Island and Crane’s Beach. They are not like commercial cranberry bogs that you see flooded with several feet of water. The wild bogs grow in only a few inches to a foot of water, depending on the season.
A wild cranberry bog would explain why we had only found the roots of mostly a single type of vegetation embedded in the clay. These would have been from the cranberry plants that are only a few inches tall.
So probably American Indians and later colonists harvested this bog for hundreds of years with horses and ever-advancing cranberry rakes whose wooden tines left scratch marks throughout the bog.
Sandy did some research and discovered that cranberry harvesters used to use double handed rocker scoops that they would sweep back and forth in front of them while they waded through the shallow bogs. They would take a step, dip the long-fingered tines below the plants, then rock them back to pluck the berries which would roll back into the scoop. This would have accounted for the short gait of the parallel tracks. These rocker rakes were invented in 1830.
So we can surmise that sometime after that date a group of people had finished harvesting the cranberries in late September, then a series of storms had blown wind off the tops of the nearby dunes burying the tracks and causing the dunes to migrate and fill in the bog.
The sand from the overlying dunes would have protected the tracks, wood, metal and scrape marks in the slightly compressed clay. Then, the series of storms and high tides we had this winter washed away the overlying sand, revealing the tracks glistening in the still-moist clay for the first time in at least 180 years.