July 14, 2020 - Sherborn

Welcome to Susan's Bay Circuit Diary! This blog follows my adventures with my dog Sulu hiking the Bay Circuit Trail.  To get new posts in your inbox, please subscribe (see the little "subscribe" oval above). The rest of the past posts can be found using the little menu on the left.  If you are curious how this all started, go here.

There was a brief break in the heat wave that coincided with my availability and Sulu and I took advantage of it to go back to Sherborn to the storied Ring of Fire segment of the BCT. This might be the most geologically interesting part of the whole BCT and certainly to date. Of course I would not know geological interest unless either I was actually walking through a geode or if the feature were pointed out to me. 

It’s taken me almost a month to get this post done! I had a vision that, by perusing some accessible, well-illustrated websites I’d be able to summarize Sherborn’s role in the geological history of the Boston area. It turns out that the geological history of the Boston area is way more complicated that I thought. There was not just one volcano, but many. The Eastern shore of North Atlantic America is the pasted-on remnant of an ancient continent called Avalonia, the rest of which is spread across Ireland, England, and throughout Europe. 

The terranes of Avalonia with modern borders for orientation: 1 Laurentia; 2 Baltica; 3 Proto-Tethys Ocean; 4 Western Avalonia; 5 Eastern Avalonia.
US: United States; CT: Connecticut; MA: Massachusetts; NH: New Hampshire; ME: Maine; RI: Rhode-Island
CA: Canada; NB: New Brunswick; NFL: Newfoundland; NS: Nova-Scotia; PE: Prince Edward Island
Europe: IE: Ireland; UK: United Kingdom; FR: France; BE: Belgium; NL: Netherlands; DE: Germany; PL: Poland (Wikipedia)

The join is a volcanic (formerly) hot spot. I really had no idea how much volcanic remains there were in the Boston area. My impression was that the land was formed by the Ice Age (true) but it ended there. Here’s a quote from the Sherborn Citizens Action Committee website, which I will hyperlink for the benefit of people who know more about geology than I do. The research process was quite humbling. 

Trail map: from D to E - you'll see some landmarks in the quote below on this map

 A major regional fault, or fracture zone, runs north-northwest across Sherborn. The fault, which is now inactive, runs from where the railroad tracks cross the Charles River near Rocky Narrows, along the western boundary of Great Rock Road and Pine Hill and beneath Indian Brook north of Lake Street. This ancient fault marks the western boundary of the Boston Basin, which is lower than the surrounding area to the west and north. Rocks to the east of the fault are younger than the metamorphics to the west, and include extensive volcanic rocks (the Mattapan Volcanics) deposited as ash fall tuffs (rhyolite). Interbedded with the volcanic rocks are sedimentary rocks which have been lightly metamorphosed (the Cambridge Argillite and Roxbury Conglomerate). These rocks were later intruded by younger intrusive igneous granites, such as the Dedham Granodiorite. The complex can be seen at Pine Hill and on Great Rock Road (Town of Sherborn 1996). 

These are the rocks

The Boston Basin. 

Anyway, the trail report! I started at Pine Hill Elementary School where I had parked last time I was in Sherborn. It was great to be back on the trail. Sulu found the trail head for me. I could see evidence of the recent heavy rains in the debris on the trail. I remembered the bug spray! Unfortunately the bug spray does not address the spiderwebs at all and is not a complete panacea when it comes to small bugs that want to climb up my mouth and nose. I forgot the sunscreen! I also forgot that Sherborn does not have water features for Sulu, so despite most of the trail being shaded, he got quite warm.

This trail must be well tended, because I saw minimal invasive plants. The entire walk was on Sherborn Town Forest land, and there was minimal road walking. The trail was generally well signed although I would have quit the BCT project long ago if not for the Alltrails app. Most of the trail was pleasantly wide thanks to what that the BCT guide says is their origin as cart roads.

No wonder he got hot: look how furry he is! Also, cart road.

It made for a great, people-free hike. Towhees were calling everywhere in the woods, and I saw a few black swallowtail butterflies. 

Surprising number of colorful fungi

The top nature surprise was this tree.  The leaves are distinctive, but a web search was inconclusive.  I am fortunate to have a degreed forester in the family, and she identified it as American chestnut. I had believed the species extinct because of the chestnut blight, but no! It's like the elm, gone, but not gone.  Chestnuts reach the height of small trees before they succumb to the blight, then regrow from the root. I saw several on my walk paired with dead small trees growing from the same spot.

Our route skirted the modest summit of Sherborn’s Mount misery. This is the second Mount Misery I’ve encountered so far on the BCT. Curious. No “Mount Ecstasy" anywhere. We turned around at Rocky Narrows Reservation, which appears to be a joint holding of Sherborn and the Trustees of Reservations, which means it will be on leash. My next time in Sherborn will be a meandering walk through Rocky Narrows. I’m waiting for both the heat and my domestic responsibilities to subside.

Previous Post                                                                                                          Next Post