Planes and topography
Refer to the attached topographic map. The area represented is a portion of the New
Baltimore, Pa. 7.5-minute quadrangle. North is towards the top of the page in landscape
view. Assume a scale of 1 in. = 500 ft. The following data refer to the station numbers
marked on the map:
Sta. 1: contact between Ordovician sandstone and Silurian black shale. Attitude of
contact: N43W 45SW. No diabase present.
Sta. 2: contact between Silurian black shale and Devonian limestone. Contact orientation:
N48W 55SW.
Sta. 3: unconformable contact between Devonian limestone and Oligocene basal
conglomerate. Overlying strata horizontal.
Sta. 4: gradational contact; conglomerate to sandstone.
Sta. 5: gradational contact; sandstone to shale. Upper Oligocene gastropods are present in
the shale.
Sta. 6: contact between Silurian black shale and Ordovician sandstone. Contact: N40W
vertical.
Sta. 7: contact between Silurian black shale and Devonian limestone. Attitude of contact:
N47W 75NE.
The dashed contacts shown in the eastern half of the map on the west side of Lick Run
mark the limits of a Triassic diabase dike as determined by abundant float on the
hillside.
Exercises:
1. Determine the strike and dip of the diabase dike. What is its thickness?
2. Utilizing all available information, construct a complete geologic map. Assume the
contacts described above are planar parallel to strike across the map area. See
projecting_planes.pptx and Marshak and Mitra section 3.4, p. 49 for further instruction on
projecting contacts onto the map. See Davis et al. Part III B, p. 687, for description of
components of a geologic map.
3. Construct a topographic profile and geologic cross section from A – A’.
4. Determine the total thickness of the Oligocene section.
5. What type of macro-scale structure is present?
6. Write a brief geologic history of the map area.