Robbins Hill is the highest point in Chelmsford and is reputed to be "made out of limestone". I did see some lime quarries over in that part of Chelmsford today but clearly the hill is mostly made of granite. The second site I saw today (middle blue outline in the map fragment below) is on a southern shoulder of Robbins Hill. I was heading up and across the southern flank of the hill and glanced back more westerly and saw what looked like it just might be a rock-on-rock, so I turned in that direction to get a closer look. As soon as I stepped over a stone wall, there was a platform pile (shown above) - broken down but with that blaze of quartz which you can see in this second picture.
Glancing uphill, I could see other low ground piles, somewhat evenly spaced, arranged on the slope. These are marker pile site characteristics.
The piles were mostly low to the ground incorporating elongated or "pointer" rocks. All with rust covered rocks, most with a single piece of quartz.
I have come to believe that rust stained rocks are usually an indication of fire. Tim Fohl and Jic have done the experiement and we are pretty confident that fire causes oxidation of iron in the rocks around here. So these pile today all looked to me like they had been through a fire - or had a fire burnt on top of them. This is one of things I speculate was common at marker pile sites. One type of marker pile seems to be a composite like this: burnt (rusted) rocks combined with quartz blazes - sometimes with pointer rocks sticking out from the pile. There were several other beautiful things at this site, I'll put them in the next post.