Mike Nonnemacher’s greatest passion is to wander off the beaten path—the more difficult the hike, the better.

In a recent hike, Nonnemacher parked at Glen Onoko and headed north along the Lehigh Gorge Trail. After perhaps one hundred yards, he had enough of the easy trail, so he crossed the railroad tracks and headed up the side of the Broad Mountain.

There, Nonnemacher discovered about a dozen drilled and split boulders. He contacted me by writing, “It's unbelievable all the work that went into these rocks just to let them sit there. Finding all these rocks together is like finding an abandoned workshop that the workers suddenly abandoned.”

I met with Nonnemacher and followed him to the work area as he deftly stepped from one bolder to another, scampering up a sever incline littered with dry leaves covering hiding crevices between the rocks. Although there were plentiful trees to grab, nearly half of those were dead and cracked under my weight. Probably few people had come this way, otherwise more of these dead trees would have been pulled down by other hikers.

Although steep, the climb wasn’t far before we reached a major rock outcropping with boulders piled one upon another. Nonnemacher pointed to a large stone, perhaps two feet in width that had ten grooves in it. The grooves were in a line, with each groove looking to be about one inch wide and around four inches deep and roughly on six-inch centers.

Looking around the site, Nonnemacher pointed out several other boulders with holes, this suggested that the grooves were really holes that had split in half. Actually, that seemed to be the function of this work area. It appeared that at one time, workmen drilled holes into the rocks to split the rock into the right size construction blocks, perhaps for building the Lehigh Canal.

We looked at the holes. Nonnemacher thought that they were not round but may be some type of polygon, perhaps a triangle. The holes also seemed to taper. It was also interesting that they were only four inches deep, although the boulders were sever feet thick.

Nonnemacher suggested that they were used to build a nearby lock on the Upper Division of the Lehigh Canal. We were theorizing that, because the boulders were so heavy and there were likely to be a number of outcroppings along the mountain, the workmen would prepare stones as close to the lock that they were working on as possible.

After splitting the stone to shape, the workmen could have used a long lever to flip the stones down the mountain and then haul them by sledge to the lock. The easiest way to accomplish that would be to wait for winter, and after the Lehigh River, which was then dammed had froze, use a team of horses or mules to pull the sledge across the ice covered river.

Nonnemacher had wondered how the 19th century workmen were able to cut the holes and crack the stones without powerful machinery. I set out to research how it could be done.

A number of possible answers came to light after several hours of research. It seems, people have been splitting boulders for thousands of years, in fact many of the techniques the Egyptians used to quarry, transport and erect stone for their pyramids and obelisks still haven’t been equaled.

Although I’m not sure how the workmen on the Lehigh Canal actually split the rocks, most likely they followed the practices of the day to drill the holes and to split the rock.

The process of splitting a rock is sometimes called sledging, and a tool that was used to perform the sledging was the sledge hammer. The workman would draw a line across the stone and mark a location fro a hole every six inches. Then he would use a steel drill that looked like an iron bar, slightly less than an inch in diameter and about a foot long, that often had an octagonal cross section and a cross-shaped cutting edge at its tip.

To drill the hole, the workman would place the cross point of the steel drill on the mark and strike the end of the tool with the sledge hammer. The workman then rotated the steel drill one eighth turn and gave it the next hammer blow. This continued until the hole filled with fine particles, which were removed with a spoon-like device. Going to a depth of about four inches was considered adequate.

The sledging could be a one man or two man operation. If one man performed the operation, he would often change hands because the weight of the sledge hammer was fatiguing. Often the woman tied a leather chord to the handle of the sledge hammer and tied it to his wrist for support and to prevent it from sliding out from a sweaty hand and injuring someone nearby.

When two workmen performed sledging, one held the rod while a second workman used a long handled sledge to strike the rod. Needless to say, this was extremely dangerous.

When better equipment became available, holes were drilled using hand drills similar to the type used in beginning wood shops. Later, larger drills were designed where the workman could sit and turn a crank.

Once the series of holes was installed, it was time to split the stone. The traditional method used a wedge and feather. The feather is a half round steel rod. Two feathers are placed into each hole and the wedge is inserted between them. The hammer is used to tap each wedge as the workman goes from one side to the other across the hole. The process is repeated until the boulder cracks.

Two other methods have been used to split boulders but are not as easy, quick or accurate. One method uses a blast of gunpowder, the other method uses quicklime. Quicklime is placed into the hole, mixed with water, and the hole is plugged. The chemical reaction creates heat and causes the mixture to nearly double in volume. This creates enough force to split the rock. A similar technique, placing quicklime in cracks in the stone is said to have been used to remove rock from the Hacklebarnie Tunnel Mine.