Windy Hills Metamorphism EarthCache

This is an Earth Cache located off of Kirkwood Highway just East of Newark, Delaware. There is no physical cache container located here. Logging requirements are listed at the end of the description.

Considered one of Delaware's most famous Piedmont outcrops, the Windy Hills Bridge outcrop is composed of mafic and felsic gneiss of the Windy Hills Gneiss. Always remain aware of your footing. Be careful and have fun! Feel free to post a picture of your visit to the Windy Hills Bridge Outcrop.

MAFIC is a word derived from MAgnesium and Ferric which refers to iron. Therefore mafic rocks are rich in iron and magnesium which makes them high in density and dark in color. FELSIC is a term derived from the mineral feldspar. Both kinds of feldspar are rich in the minerals silicon (Si) and aluminum (Al). Felsic rocks are generally light in color and lower in density than mafic rocks.

Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form". The original rock (protolith) is subjected to heat (temperatures greater than 150 to 200 °C) and high pressure causing profound physical and/or chemical change.

The layering within metamorphic rocks is called foliation (derived from the Latin word folia, meaning "leaves"), and it occurs when a rock is being shortened along one axis during recrystallization. This causes the platy or elongated crystals of minerals, such as hornblende and plagiocase, to become rotated such that their long axes are perpendicular to the orientation of shortening. This results in a banded, or foliated rock, with the bands showing the colors of the minerals that formed them.

Much of the layering in the outcrop is regular and is 8 to 10 inches thick. At the contact between these layers there is evidence of partial melting. Overall, strikes of foliations of the mafic and felsic layering in these outcrops are 70-75 degrees east of north and the dips are a steep 80-85 degrees to the southeast, or almost vertical.

If you look at the amphibolite rocks toward the west end of the outcrop and find layers with very tight, strung-out folds within the layers, you will see single, light, coarser grains that have been rotated and sheared out into very thin white stringers. This is evidence that there has been intense shearing and stretching within those layers. Notice that the darker layers do not contain similar features.

To log this cache send me an email with your answers to the following questions:

1. How thick is most of the layering of the rocks in this outcrop?
2. Since the lighter layers of the rock show more shearing and stretching than the darker layers, which of the two do you think was stronger during metamorphism?
3. You will see evidence of cylindrical boring in the rock in order to analyze rock composition. How many holes were drilled?
4. In your estimation, is there more felsic or mafic rock present in the whole outcrop? 

Pictures of your visit are not required but are always enjoyed!