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Glacial Erratic

A cache by amgleason Send Message to Owner Message this owner
Hidden : 10/09/2007
1 out of 5
1 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

This is an entry level cache. One needs only to walk a short distance on city sidewalks to get to this geologic feature. The erratic rests on Fitchburg’s upper common. Routes 2A and 31 are within 25 yards of the boulder. Be careful of vehicle traffic.

Parking can be found either at the Fitchburg Post Office on Main Street or on street parking at parking meters.
Rollstone Boulder is a local landmark in the city of Fitchburg, MA. The boulder is located on the northwest end of the common on Main Street. There is quite a bit of history behind this glacial erratic. Before that history is discussed however, one needs to know what a glacial erratic is.

Glacial erratics come from glacial deposition. Glaciers are solid masses of ice. Glaciers exist when climate conditions are perfect for their formation. About 10,000 years ago such conditions existed in Massachusetts. The temperatures stayed cold enough for literally thousands of feet of snow and ice to accumulate. In fact probably 2,000 to 3,000 feet of ice sat upon Fitchburg. This huge mass of ice is known as nature’s plow because it can plow and move huge amounts of rocks and sediments. A glacier will move. It moves slowly, perhaps just inches per day, and picks up a great deal of rock and sediment. This rock and sediment is known as its load. This load can be transported great distances. This includes rocks and sediments of all sizes from huge boulders to specs of sediment. This load is virtually carried either on top of the glacier, or embedded in its ice from top to bottom. This load is directly deposited where ever it was transported when the glacier melts. A glacial erratic is just such a deposit.

What makes an erratic a particularly interesting glacial deposit? Well, first glacial erratics are usually very large. Such is the case with the Rollstone Boulder on Fitchburg’s common. Additionally erratics are made of different rock on which they presently sit. In other words they came from a different location than where they now rest. This is normally quite obvious. For example the Rollstone Boulder is porphoyritic granite and it was found resting on Rollstone Hill, which was once a granite quarry in Fitchburg, which is made up of very different granite. The Rollstone Hill granite has much more iron in it than the Rollstone Boulder. One also finds a significant amount of schorle tourmaline, a black glassy mineral, in the granite on Rollstone Hill, but one does not find it on Rollstone Boulder. In the case of a glacial erratic one can certainly use the phrase, “one of these things is not like the other.” Finally an erratic can be found many kilometers away from where it was picked up by a glacier, and this is the case with Rollstone Boulder. (Earth Science Australia, Glaciers, 2007)

Rollstone Boulder weighs approximately 100 tons. It is made of porphyritic granite. It currently rests on Fitchburg’s common, but it didn’t always. In fact if you look in a westerly direction you will see where it actually was deposited by the last glacier that came through Fitchburg about 10,000 years ago. Look up to Rollstone Hill, it’s often easy to identify. It’s about one mile away. One can usually see that Fitchburg High School seniors paint their year of graduation on the hill. This is approximately where the Rollstone Boulder was deposited by the glacier. (Andrienne)

It is believed that Rollstone Boulder came from the area around central New Hampshire, perhaps Bedford or Concord, New Hampshire. This means that the last glacier moved this large rock approximately 100 miles. If one takes a close look at the boulder one will see that this granite has some oblong crystals of white feldspars, something that the granite on Rollstone Hill does not have. (Kirkpatrick, 1971).

How did the boulder get to its present day location? Well as can be imagined moving this big boulder in one piece was impractical. If the boulder was going to be moved it had to be done in pieces, this could only be done by fracturing it. This process of fracturing has an interesting story behind it and demonstrates that fracturing the boulder was not very easy to do. On September 6, 1929 the McCauliff Quarry Co. painted the boulder with red and white numbers so that after they fractured and moved the boulder they could put it back together. They then dug away and blew up the ground beneath the boulder allowing it to drop 15ft to a ledge below. The boulder did not break apart as they thought it would. They had to eventually use dynamite to blow the rock into pieces so that they could load it on to trucks. They took the pieces of the rock from the top of Rollstone Hill and transported them to the upper common. The boulder was reassembled by Mark LeBlanc at a cost of about $364.74, which was probably a fairly large sum at that time. The assembly was completed around November of 1930. A side note here is that LeBlanc was never reimbursed for his efforts and money.(Andrienne)

The history behind the boulder as a landmark is a long one. Indians and early white settlers used the boulder on top of Rollstone Hill as a landmark during their travels as far back as the early 1800s. Later, curious hikers climbed Rollstone Hill just to see the boulder. Professors and students of geology hiked the mountain to study it.(Kirkpatrick)

One wonders if passers by in vehicles ask the question, “What is that big boulder on the common all about?” Well, now you know that the boulder is about Earth’s history and the last ice age that was in New England. You also know that people are affected today by Fitchburg’s glacial past and demonstrate that by moving a glacial erratic from its original location to its present day location, no easy task.

In order to get credit for this cache you must do the following:

1. Read the plaque.
2. What is the exact weight of the boulder according to the plaque?
3. The plaque was placed on the boulder at the time of its reassembly on the common. At that time the local people thought that the boulder came from a different location other than Bedford or Concord, NH. The location stated on the plaque is wrong. Where does the plaque say that the boulder originally came from?
4. Estimate the circumference of the boulder.
5. E-mail your findings along with a picture of your GPS in front of the boulder.

Visiting this cache site accomplishes several Massachusetts’ required teaching standards in Science and Technology.

Massachusetts Frameworks:

• Give examples of how the surface of the earth changes due to slow processes such as erosion and weathering, and rapid processes such as landslides, volcanic eruptions, and earthquakes.
• Describe and give examples of ways in which the earth’s surface is built up and torn down by natural processes, including deposition of sediments, rock formation, erosion, and weathering.
• Explain and give examples of how physical evidence, such as fossils and surface features of glaciation, supports theories that the earth has evolved over geologic time.
Inquiry Skills:

• Observe the world from a scientific perspective.
• Articulate and explain the major concepts being investigated.
• Identify and use navigation features of a browser
• Using a browser, “bookmark” a Web site for future reference
• Using e-mail create and send a message
(1996 – 2007). “Earth Science Australia”: Geological Society of Australia. Retrieved September – December 2007: (visit link)
Clark, Andrienne. “Rollstone Boulder didn’t want to roll.” Fitchburg Sentinel and Enterprise. One page, date unknown.
Garboden, Cliff. (1988, August). “The Rollstone Boulder.” The Boston Globe Magazine. P.14.
Kirkpatrick, Doris. (1971) The City and the River, Vol. 1. Fitchburg, MA: Fitchburg Historical Society.

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