The coords put you on a public sidewalk outside a business in Canton, NC. You will need a measuring device (e.g. - a ruler with metric units) to complete this Earthcache. Parking is close by.
Clast sizes
When rocks mechanically weather--from the action of ice (freezing and thawing) and/or the prying of plant roots--fragments of those rocks break off. Those fragments, called “clasts,” come in differing sizes (see chart) that continue to break down over the years.
(Source: http://scienceviews.com/geology/sedimentary.html)
The clasts can be transported (eroded) by water, wind, gravity, and glaciers to low spots (e.g. - oceans) where they can accumulate, compact, and re-form into clastic sedimentary rocks.
The larger the clast, the more energy it takes to move it. Sand, silt, and clay can be transported by wind as well as water, but on the other hand, pebbles, cobbles, and boulders are too large to be picked up by wind. Boulders and cobbles need the fast-moving water of streams to erode. Glaciers can move all sizes of clasts, but there is no evidence of glaciation in North Carolina.
Angularity of Clasts
Streams act like giant rock tumblers as they move rock fragments. The heavier clasts roll along the stream bed and smack into each other wearing away sharp edges and making the clasts more rounded and smooth. The longer the clasts are transported, the more round they get.
Angularity is the measure of the roundness of a clast. Here is a simple chart:
(Source: https://courses.lumenlearning.com/wmopen-geology/chapter/outcome-sedimentary-rocks/)
Fragments that have mechanically weathered more recently and/or not moved much tend to be more angular--have sharper edges. Fragments that have moved a long way from their source rock tend to be more rounded.
Tasks
Examine the rocks composing the facade of the building. If you have small children with you, be aware of traffic.
1. Using your ruler, measure 5 of the clasts in the side of the building. What is the average size of the clasts you measured?
2. Using the chart above and your measurements, what is the average clast size used in the facade--boulder, cobble, pebble, sand, silt, or clay?
3. Using the angularity chart above, determine the general angularity of the clasts in the side of the building.
4. From the size and angularity of the clasts, what can you conclude about the conditions under which these clasts were deposited before they were dug up and used as building materials?
5. Optional: Take of photo of you enjoying your time at this location.