Rocky Point, at World's End Park in Hingham

Rocky Point is in the World's End Park in Hingham. This park is really one of the most beautiful hiking places in the Boston area. Rocky Point has a great deal of exposed rock, showing several layers of volcanic rock on top of one another.

View along the North side of Rocky Point, showing the variety of
exposed rocks visible

View along the South side of Rocky Point, looking across
the Wier River towards Hull


Below you see a picture of an outcropping found in the middle of a forest. Can you guess which type of rock this is? What evidence would you use? What more information would you need to identify the rock? This is from the same outcropping - a small chip was removed. This rock is a fine-grained dark colored rock, perhaps basalt. This shows how important it is to look at a fresh surface, since weathering can dramatically change the color and appearance of the rock's surface.

In the picture below, you'll see two different types of rock on either side of a basalt dike. Which of these trock types do you think erodes more easily? Can you think of reasons why it might erode more easily than the other rock types?




There are 3 volcanic rock types shown in the picture below: basalt (closest to the water), then a type of green volcanic "conglomerate", and then a lighter grey-pink volcanic "conglomerate". The volcanic conglomerate forms as fragments of lava and rock are blown out of a volcano. They land on the flanks of the volcano, with the biggest pieces landing closest to the volcanic vent and smaller, finer fragments carried further away before they settle to the ground.

Note that the picture looks down upon an exposed cliff - these 3 volcanic layers are tilted downward, toward the water.

Do you think this was the original orientation of these rocks?

Try to draw a picture showing how this outcropping was formed.

The next two pictures show two different types of volcanic "conglomerate" - rock formed by cemented volcanic ash that includes bits of other rock. The picture on the left is contains amygdules - bubbles of gas that leave behind mineral deposits. The original holes in the basalt form from gas bubbles in the molten rock, and the empty holes become filled with other minerals from fluids that later move through the rock (such as groundwater).

The picture on the right contains pieces of basalt. While both of these types of rock are formed from ash, their composition and appearance are very different. Can you describe how these two rocks formed differently?

In the two pictures below you can see giant pieces of rock that got trapped in the ash flow before it all solidified into rock. Can you describe how this process might have happened?

In the pictures below, you see a series of volcanic rocks. Notice that there are at least three different types of rock here - black, green and tan. Notice also that the rocks occur in layers. Try to describe the process that led to these different rocks being formed in these layers, one on top of another.

Here are two rocks that look similar, yet formed very differently. One of them is the Roxbury Conglomerate, which formed by weathering and erosion of sand and pebbles being deposited in a stream or river bed. The other is a form of volcanic conglomerate, in which small pebbles got caught up in an ash flow, which eventually hardened together into one rock. Can you figure out which is which? What clues did you use to decide?