Tuesday, October 23, 2018

Wrentham begins to reveal itself - Birchwold Farm and the Wrentham "Pavement"

I drove a bit further from the highway to a place on Rt 121 in southwestern Wrentham called "Birchwold Farm". Previously, in this direction, I got to Red Brush Hill and was disappointed. This time, I went a little further to this place, stepped into the woods and found rock piles. That's always nice.
This first rock pile combined some interesting "geologies" seen in other places. The tourmaline granite, familiar from Sterling:
And the red rock of the Wamsutta formation, familiar from Randolph:
I think the red rock is bedrock here. I stepped over towards the parking lot (having parked south of it on 121) and noticed a loose "pavement" mound:
 This is 15 yards from the parking lot. Another view.
It was tempting to rush off south into the conservation land but I was having such success, I turned back to look along the bluff that overlooks the open field there and found other beaten down mounds. No need to look further, they are right there in the bushes. In fact the whole 'bluff' had loose mounds forming a pavement and overlooking the lower wetter areas to the southwest:

The "gem" of these, from above:
And from below:
And from a distance, easy to see from the field below:

The observation is that loose mounds along a bluff, overlooking a wetland, are the same type of mound that I saw last time in Wrentham, just north of here over by the store outlets. I compare these to what I called "Ravine Culture" from up north, closer to New Hampshire. Loose "pavement" along bluffs occur throughout Massachusetts - from Webster woods in Falmouth to East Wachusett Brook in Princeton and Blood Hill in Ashburnham. I think they are harder to see when there are newer rock piles around to distract one's attention. But down here in Wrentham, they are a pure expression - the only game in town. And so you notice them. 

To be honest, there were fields nearby and not a very strong argument against "field clearing". To do what I can to argue the case (1) argue from similar architecture nearby; (2) argue the quantities of local bedrock in the mound; (3) argue from the mounds being uphill from the field; (4) argue that field clearing creates mounds, not pavements; (5) argue that field clearing produces rocks of different sizes and that these mounds are composed of rocks that are all about the same size - so the wrong size distribution of component rocks. At the end of the day, these arguments contain useful observations but also keep the "field clearing" hypothesis alive.

I walked around for a bit longer, it was late in the day, and I did not get as far south as I hoped. There is plenty more exploring to be done along that brook, which is one of the brooks leading down to Diamond Hill Reservoir, and further waterways leading down into Pawtucket, Rhode Island. From the looks of it, Pawtucket and Fitchburg are similar in being the meeting place of many brooks and rivers. I will try to hunt out those headwaters.

I had a pleasant hypothesis confirmation when I went a little eastward into a north-south valley [right hand side of the map fragment] and looked to the left along the slope I was coming down, seeing nothing, then looked across the valley to the far slope and a little uphill - just to be scanning the flanks of the headwater valley - and seeing another tumble of rocks spilling over a bluff.
Since it seems to be a well defined type of mound, common in Wrentham, let's give a name like Wrentham Pavement. Other suggestions?


Anonymous said...

I tried to find a fancy European name for cobblestone roads but came up empty. I have wondered the imagery this pile type would produce viewed from above, I'm imagining it to be nazca line like.

pwax said...