This column appeared in the Summer 2012 issue (Vol.1, No.2) of The Recorder's Outdoor Adventure Magazine
If you were to jump into a time machine and set the dial back to 200 million BCE you would emerge into a very unfamiliar world. At this point the great supercontinent Pangea was just beginning to fracture and its sections drift away toward their modern positions. This process of ripping a continent to pieces is known as “rifting,” and it has some fairly interesting consequences.
Prior to the rifting of Pangea all of the Earth’s landmasses were connected. Once rifting started, however, large gaps started to form on the surface. Initially these gaps were filled with lava that welled up from the depths of the Earth’s interior to fill the void. This process is quite analogous to the everyday filling of a wound with blood to form a scab. The only difference is that the Earth filled its wounds with rock, traces of which we can easily find to this day.
One particularly large rift eventually matured into a little feature of the planet that we like to call the Atlantic Ocean. There were other places where rifting was not quite as severe, and that is where the local flavor of this article comes into play. You see we live in one of these lesser rifts. We are, in a sense, populating one of Earth’s old stretch marks, the center of which is filled with the flowing waters of the Connecticut River.
Now the thing to remember is that the rifting process was not a sudden one. The tensions would build in the rock until a fault occurred, then the lava would pour out over the surface of the land in layers of great depth. Then things would quite down for centuries before another great fault would form and result in another great lava flow. In the time between lava flows the processes of weathering and erosion would lay down beds of sediment that, once buried, would lithify (solidify) into sandstone.
This layering of tough lava rock (a formation we now refer to as basalt or taprock) with softer layers of sandstone set the stage for a dramatic landscape feature that we know today as the Metacomet Ridge. In the final stages of rifting the layers of this rocky cake were fractured and then tilted at odd angles to the ground. Then the process of erosion set about the task of destroying the rock that it had helped to form in the first place, which resulted in some truly beautiful “mountains” in our area.
One of the most iconic features of the landscape of southern Franklin County is Mt. Sugarloaf in Deerfield. The red sandstone (known as arkose sandstone) represents one of the bottom layers of the cake. It also provides the best illustration of the fracturing and tilting Earth’s surface as a result of rifting. From Rt. 116 you can easily observe the fact that the rock strata (layers) are all parallel with each other, but are not parallel to the ground. Just imagine the force required to lift and tilt something so large.
From the summit of Mt. Tody the effect is even more dramatic. “Mt. Sugarloaf” is actually a much larger geological feature than is initially apparent. The southern peak is usually what is referred to as Mt. Sugarloaf, but there is also a northern portion that is called the Pocumtuck Range. Both mountains are part of the same set of sedimentary layers that have been tilted by the process of rifting. Hiking Mt. Sugarloaf is as easy as driving to Deerfield, parking your car, and walking up the road to the summit.
For me, however, the most fascinating example of rifting and erosion can be found in a little place known as the Horse Caves. Located on the eastern slope of Mt. Norwottuck (in the Holyoke Range State Park) this geologic gem was a favorite destination for me when I was a boy. All I had to do was walk across Bay Road and up into the woods and I could be to the Horse Caves in under 30 minutes.
If you’re willing to drive down Rt. 116 to hike up Mt. Sugarloaf, then perhaps you will be willing to go just a little further and find your way to the Notch Visitor’s Center in Amherst. There you can park your car and take a lovely walk to the Horse Caves.
There are two routes that you can take and I will leave it up to you to decide what you want to do. As you leave the back of the Visitor’s Center you will find yourself on a single trail called the Metacomet-Monadnock (M&M) Trail (marked in white). Ten minutes of walking will bring you to the first choice you have to make: turn right and continue on the M&M trail, or continue on straight on the orange Robert Frost trail.
I usually go straight on the Robert Frost trail, then take a right at the first big “T” intersection and head up the hill. This trail can get a little steep, but not for too long. Then I find myself at another confusing intersection where the orange Robert Frost trail heads to the left to Rattlesnake Knob. Here you want to go right and follow the white M&M trail. After a short, upward hike of another 10 minutes or so you will find yourself at a very dramatic rock face.
The M&M trail will continue up through a crack in the rocks and then make its way to the top of Mt. Norwottuck. But if you are willing to take a very short detour you can see the area that I always knew as the Horse Caves. Clearly the product of water erosion, the “caves” are small, but you can actually go inside one of them. You will also be able to see the coarse conglomerate sandstone that form yet another layer of the great cake.
If you then return to the M&M trail you can go to the summit of Norwottuck (which is made of basalt) and look north to see Mt. Sugarloaf. After a wonderful break atop this mountain you can continue on the M&M trail and find yourself rejoining the Robert Frost trail down where you originally decided to go straight instead of right. It is a wonderful loop that will keep you busy for a couple hours, reward you with fantastic views, and help you understand some of the geological history of our area.