The Geology of Kent Falls State Park
Outline of Geology Found at Kent Falls State Park
Rock Types Found on Main Trail
- Dolomitic marble
- Schistose marble
- Stockbridge marble
- Basal Marble Member of Wallomsac Schist
Minerals of Interest
Interesting Geologic Features
The most obvious feature at Kent Falls is, of course, the falls. Actually, they are a series of falls and cascades. Multiple falls and cascades, such as these, generally form where the bedrock contains alternating hard and soft layers. This part of Connecticut was once made of coral reefs, offshore from the northwestern part of the state. As the Iapetos Ocean closed when Europe and Africa moved our way, these reefs were squeezed and buried under other rock. With increasing heat and pressure, the minerals in these rocks recrystallized, and the former coral reefs turned to marble. Sand and mud around the reefs formed the impurities in the marble that cause some layers to be more resistant to the effects of the flowing water.
Figure 1. A double pothole worn into the rock by swirling pebbles. Notice the rock to the right of the potholes is nearly vertical. Look for more potholes as you walk along the trail.
Walk up the trail along the right side of the falls. The first two cascades drop over flat-lying layers of marble. But farther up the trail, at the third cascade, the rocks have been turned up on end. On the other side of the stream, small rocks trapped by swirling water wore a double pothole out, into the rock. The potholes are now combined (Figure 1). These rocks were possibly rotated from the horizontal when the nearby fault was active. The fault lies between here and Dugan Road at the top of the series of cascades and falls, but it is not visible along the trail.
Figure 2. This block of schist (notice the shiny mica grains), contains a vein of lighter-colored marble.
After passing a side trail to a lookout of the falls, look for several boulders on the right side of the trail. These are gray schist, and one has a marble vein in it (Figure 2).
Figure 3. A boulder of very soft marble, which feels like sand where it is not covered by moss.
At a 90o turn in the wooden trail, look for a rock to the right that is nearly covered by moss. Touch the white, exposed area. Here, the marble is very sand-like, because it is weathering easily (Figure 3). Marble like this, in the stream, would not last very long.
Figure 4. The falls formed in this massive rock where two parallel fractures occur. They are hidden by the water, from this view.
When you reach the next overlook, sit down on the bench and study the rock on either side of the falls. It is eroding between two parallel fractures that are not quite vertical. They give the impression that the falls are not upright (Figure 4).
The rocks forming these falls are not marble, at least not at the top.
Figure 5. These obvious lumps in this rock are garnets. They are more resistant to weathering than the other minerals making up the rock, resulting in the noticeable, differential weathering.
Continue on up the red trail to the road, walk on the left across the bridge, then walk down the Red Trail. Look for a large, low outcrop, a little off the left side of the trail. This is the rock where the high falls in Figure 4 drop along two fractures. Notice the lumpy rock (Figure 5). Although the lumps look light-colored at first, upon close examination you will see that they are dark-red. These are garnets, our state mineral. The rock is gneiss, made up of bands of different minerals.
Continue on down the trail towards the parking lot. The rest of the trail has few rocks to see, but is a pleasant, downhill stroll through a nice forest. Look for a variety of plants, and occasional small animals.