Thursday, February 01, 2007

False Outcrops - at "The Desert" Marlborough, MA

At another location in the Marlborough/Sudbury conservation land, in a more obscure location than the site I described yesterday, there is a site built into the parallel ridges of bedrock outcrops that run more or less north-south. I have visited this area before and commented on how the outcrops look like rock piles. I noticed the same thing again: the outcrops seem to be enhanced with some rock piling.
The ledges contain jumbles of rocks which could be frost broken pieces of the outcrop; but mixed in with them there are also pieces of glacial cobbles. Here is another ledge:
In this detail of the left (northern) end you can see rounded rocks as well as flat faced sharped edged bits of bedrock. The round ones are glacial.
The ledges all run in the same northerly direction, parallel to each other. There was one stone wall running in the same direcrtion as the ledges, starting at a big rock and running north following the ridge. But the wall was broken into segments. In the next picture, I am standing on the big rock photo'ing to the north. If you look carefully there is a suspicion of a zig-zag at the beginning, a break, and another segment. There are two other segments, out of view, further along.
Here are the three segments.
By the time you get to the last one, it is little more than a rock pile. Then, curiously, up near the beginning of this wall, off to the side was another rock pile parallel with the wall (you can see the first wall segment in the background):Note there is a bit of ledge supporting this pile.

Here, the rock piles are imitating the ledges - as if the outcrops only provided part of the "solution" with a few additional false outcrops needed to complete the site. The stone wall also seems to be trying to immitate the shapes of the outcrops or at least runs in the same direction. Altogether an interesting combination of artificial structure and natural geology.

Correction: the outcrop ridges actually run more northeast than north.

1 comment :

JimP said...

I've seen a good number of rock piles at multiple sites all over New England that were seemingly designed and constructed to imitate the shape of other natural features that appear near them -- like glacial erratics, outcrops, rock shelters, and talus caves. Mary Gage documented several examples of this at America's Stonehenge as well.