Big Rock (or Orotok in the native Blackfoot language) is a massive glacial erratic eight kilometers (five miles) west of Orotoks, Alberta in Canada. Coaxial/English Wikipedia

Rope Ends – bits and pieces on cordage. In my upcoming book Rope, I write about the use of cordage to move big hunks of rock for little construction projects like the Egyptian pyramids and Stonehenge in southern England. One theory has it that bluestones used at Stonehenge were glacial erratics — large boulders pushed by glaciers during the Ice Age that when the ice melted were left behind amidst the different local rock (the glacially-moved rock has to be different from the local rock to make it an erratic. For example, the 400-ton Yeager Rock on the Waterville Plateau in Washington is not a true erratic since it is of the same type as the rock surrounding it).  

When it comes to moving rock, glacial power is mind bending — the largest known erratic is a megablock in Saskatchewan with dimensions of 18 miles by 23 miles, or more than 400 square miles of bedrock carried or pushed along by an advancing ice sheet. This little stone chip is 100 meters or 330 feet thick in places. 

Stonehenge in 2007. Old Moonraker/Wikipedia

When 2,000-foot thick glaciers moved southward to cover the British Isles, the ice sheets pushed one or two ton rocks like they were grains of sand. Some scientists say the bluestones from Wales were transported south to the Salisbury Plain and deposited there when the glaciers retreated. The builders of Stonehenge took advantage of the bluestone lying at their feet. Of course, even if this theory is true, the bluestones weren’t all left at Stonehenge’s doorstep. They would still need to have been dragged some miles to the building site, likely on wooden sledges with long ropes to allow for plenty of workers to put their backs into it.