SANDY BEACH, COHASSET  -  42.24N, 70.80W

Sandy is the town's swimming beach. It is bordered on either side by huge outcrops of Dedham Granodiorite filled with dikes of basalt. One of those dikes was made famous in Leet and Judson's Physical Geology  text of the 1960's.  The sand is fairly fine and has a light tan color. This image was taken just after tropical storms Bill and Dan passed through. Because of that, there is a huge amount of organic matter on the beach. Normally, it is almost spotless!

GROSS IMAGE

3X MAGNIFICATION (SPACE BETWEEN BARS  = 1MM)

ROCKY BEACH, COHASSET  -  42.24N, 70.80W

No image does Rocky Beach, or Black Rock Beach, any justice. It is magnificent. Just as Sandy Beach is calm and inviting, Rocky is violent and dangerous. The surf pounds these rocks constantly. This picture was taken just after the passage of Tropical Storm Bill. The rocks had been thrown into a series of terraces leading from the water to the artificial wall that stops the rocks from covering the road. Sand is scarce here. There are tiny patches right at the water's edge, and then again at the very back of the beach. As you head from the water to the back of the beach you first move through some very dark, fine sand, which is where I collected the sample. The beach then immediately goes up at a very steep angle piled with large rocks. As you head toward the back of the beach, the rocks get smaller, and smaller until sand is found right at the wall. This beach is a geologist's paradise. The rocks are mostly granodiorite filled with basalt dikes. The granodiorite has been slightly metamorphosed, and that can clearly be seen in the boulders as the crystals change from random to banded.

GROSS IMAGE

3X MAGNIFICATION (SPACE BETWEEN BARS  = 1MM)