THINGS TO SEE
The rock face exposed at the corner of 3rd and Canal Streets north of Avenue A offers one of the most interesting and accessible views of the Turners Falls formation you can see anywhere. Notice the alternating thin and thick layers in the formation.
THINGS TO KNOW
What is a formation? A formation is a series of rock types found together that indicate an ancient environment of sediment deposition. The Turners Falls formation exposed on 3rd Street consists of repeating thin-bedded shaley sandstones sandwiched by thick and bulky sandstones.
Thin and thick = wetter and drier. The thin beds indicate the muddy bottoms of deep lakes that formed during wet periods. The thick and blocky beds originated from sediments dropped by streams running through the old lake beds in drier periods, when the lake water was gone. Thus, what we see in this alternating sequence of thin muddy lake bottom sediments and thick streambeds are wet and dry cycles that occurred, on average, every 20,000 years.
When a rock is a hard place. Where geologists see ridges, they think “hard, weathering-resistant rock.” That’s exactly what the 3rd Street rock face is. This relatively hard sandstone was once a river channel that now rises up like a small cliff because the less weathering-resistant rock around it has been worn away.
Note, however, the deep cut below the rock face-that rock is anything but hard. What does this sudden difference in rock type mean? Geologists believe the softer rock represents the bed (called lake bed #3) of a deep lake that filled the valley approximately 200 million years ago. These rocks are soft and black because they started out as an organic mud.
As a result of a natural climate cycle in the early Jurassic, the lake dried up and much of its bed was violently eroded away by invading rivers. This cycle happened at least four times in Turners Falls during the early Jurassic.
NEXT STOP
Walk south along the sidewalk on Avenue A to the pedestrian crossing. Cross the street to a stairway leading up to Our Lady of Czestochowa Roman Catholic Church.
