Every mile along The National Road, or Old U.S. Route 40, there were milestones placed to show the distance to the nearest major city. They are marked with the milage number followed by "TO B" which means to Baltimore. The first 39 miles from Baltimore to the west had milestones made of Baltimorean Gneiss that was mined out of the ground in the early 1900s to help construct these first 39 milestones.
Gneiss is a type of metamorphic rock, meaning it was melted and hardened in the earth's crust or upper mantel. The parent rock of these gneiss could have been sedimentary rock or another cooled metamorphic rock. This sedimentary rock could likely be from shale, which is calcium rich rock. Shale forms when dead organisms with shells or hard backs fall to the bottom of a lake or ocean. over millions of years, these layers become compacted and pressed to form shale. Given more time and pressure, heat builds up and morphs the shale into the following categories of metamorphic rock, depending on time, depth, pressure.
Works Cited
https://en.wikipedia.org/wiki/Old_National_Pike_Milestones
http://geology.com/rocks/gneiss.shtml
https://en.wikipedia.org/wiki/Gneiss
http://vhmsscience.weebly.com/rock-observations.html
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1. Elliott City - National Road Milestones on the first line of your email.
Answer the following questions regarding the above coordinates (N 39° 16.077 W 076° 47.695)
2. Describe the (a) texture, (b) height, (c) colors of the milestone.
3. Describe the weathering process of Milestone #10. Is there any rusting or corrosion? If so, where do you see it and why is this occurring?
Answer the following questions regarding the additional waypoint (N 39° 16.186 W 076° 48.733)
4. Describe the (a) texture, (b) height, (c) colors of the milestone.
5. Describe the weathering process of Milestone #11. Is there any rusting or corrosion? If so, where do you see it and why is this occurring?
When you have visited both sites, answer the following questions based on your answers above.
6. Which milestone has had the most deterioration due to weathering? If they were both placed at the same time, why do you think they feel, not look, completely different?
7. Based on your observations, was the Gneiss, that was needed to build these milestones, quarried at the same place or different areas of Maryland? Why do you think so?
8. What prevention techniques could you add to help preserve these national landmarks from natural weathering that haven't already been implemented?
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