Figure 8. Inclusion of layered or banded metamorphic rock (hammer is resting on this inclusion) in lighter colored biotite granite as seen along the Bear Den Ski Trail. The metamorphic rocks were invaded and undermined by the granitic rocks, with the result that pieces of the metamorphic rock were surrounded by granite. For scale, the handle of the geologic hammer or pick is about 12 inches long.
Figure 9. Picture taken along the Burke Mountain summit road of typical Gile Mountain metamorphic rock. Here the rocks dip almost vertically. For those more advanced in geology, note the pillow-like segments or boudinage structure about one foot to the left of the chisel point of the hammer. This structure is due to a stretching of the rock. For scale, the hammer handle is about 12 inches long.
Figure 10. Banded or layered metamorphic rocks with inter-squeezed granite (lighter colored material). This outcrop is located on east side of the Bear Den Ski Trail and quite close to the Burke Mountain summit road. The hammer handle, center of picture, is about one foot long.
Figure 11. Picture taken only a few yards from the Burke Mountain observation tower, along the path to the summit parking lot, looking northwest. Here you see metamorphic rocks (quartzite and phyllite) with some inter-squeezed granite. Note how the nearly vertical metamorphic rock layers bend or “wrap-around” to the right. The highly resistant inter-squeezed granite actually holds Burke Mountain up, or to be more scientific, it prevents these rocks from being worn down as fast as the surrounding rocks. For scale, see the clip board in the center of the picture.
From these relationships, what can be said about the relative ages of the two rock types? Which is the older, or first formed? Which is the last formed? If you study the above relationships for a minute or so, it will become obvious that the layered rock had to be formed prior to the emplacement of the granite. Some of the minerals now seen in the layered or banded metamorphic rocks were formed at the time of granite intrusion, but the basic “stuff” or partially metamorphosed sedimentary rock was present before the granite entered the area from beneath. So, the knowledge of the two rock types present and an understanding of their relationship to one another tells us a story of at least two events which occurred in the park area hundreds of millions of years ago.
Figure 12. Outcrop on south Lookout, summit of Burke Mountain. Distorted layers of Gile Mountain metamorphic rock. Lath-like crystals developed along some of these layers during the second period of metamorphism, that is, when the granite invaded the metamorphic rocks. For scale, the hammer handle is about one foot long.