geology

39

7. Maps and Structure

Credit is given to SERC for borrowing and modifying activities.

Goals and learning objectives:

• Understand importance of both topographic and geologic maps
• Read topographic and geologic maps
• What information do topographic maps provide?
• Identify landforms using topographic maps
• Calculate slope using topographic maps
• What information do geologic maps provide?
• Identify geologic structures using geologic maps
• Identify faults using geologic maps

Reading:
Chapter 10 of the textbook

Materials needed:
Ruler
Graph Paper
Pencil
String
Google Earth with provided topographic and geologic map overlays

Background Information:
The key information here is how to read a map and what information can be obtained from a map.
Identifying geologic structures on a geologic map is also an important activity.

True north versus magnetic north.
While not on Google maps, it is important to know the difference between true north and magnetic
north. True north is the location of the pole of rotation. Magnetic north is the location of the “north
pole,” where a compass points towards north. A map should show the angle between true north
and magnetic north; this angle is the magnetic declination. In the field, it is important to remember
that the magnetic declination must be corrected when using a map, and to check that the magnetic
declination on the map is up to date for your area.

Contour lines:
A contour is a line that shows a specific elevation above sea level. Contour lines must never cross
(crossed contour lines indicate two different elevations in one place). They must always form a
closed loop, although the loop may not always be visible in the frame of the page and the lines
may run into the margins. They will form a V shape pointing in the upstream direction when they
cross a stream. When contour lines indicate a lower elevation, such as a dip in the surface, they
will have tick marks along the downslope direction.

40

Constructing a scale:
A map scale is one of the most important features you will see on a map. Scales come in a couple
of forms, all of which give you information about how the map represents the real world. A scale
bar is one of the most commonly used scales. In a scale bar, a specified length (the bar)
represents a given distance in m, km, ft, or miles. To use a scale bar, simply use a ruler or piece
of paper or string to compare the distance on the map to the length of the scale bar. For example,
if your scale bar is 20 cm long and represents 100 m on the map, then a piece of string measuring
10 cm between two points shows that the points are 50 m apart.

A ratio scale is another common scale on maps. A ratio scale is just that, a ratio (i.e., 1:100). This
type of scale can seem confusing, but it’s actually very simple. 1 of something measured on the
map represents 100 of that same something in real life. The ratio scale is unitless, so any unit of
measurement may be used as long as it is the same on each side. 1 cm measured on the paper
map represents 100 cm in real life. 10 cm on the map represents 1000 cm in real life (because
you multiply both sides of the ratio by 10). 1 banana on the map represents 100 bananas in real
life (we will pretend all bananas are the same size)!

How to construct a ratio scale. It is very easy arithmetic!

Step 1: Zoom in to Google Earth so that you can clearly see the details of the map. You can move
the map around, but if you change the zoom, you will have to re-do your scale!

Step 2: Click on the ruler on the top of the page. Select the “Line” option.

Step 3: Select two points that are easy to identify (e.g., the football stadium and the Virginia Tech
Airport).

Step 4: Click on your first point and then your second point. You should now have a line.

Step 5: Change your units on the line to match the units on your ruler (I prefer cm, but inches will
also work).

Step 6: Measure the line on your screen using the ruler (if you have a touch screen, be careful).

Step 7: Write down the map length number that the ruler measured (you can round to a whole
number).

Step 8: Make a ratio with the number in Step 6 above the number in Step 7. DO NOT DIVIDE!
Example below.

Step 9: Now equate the ratio in Step 8 to the ratio to 1 over x. Example below.

Step 10: Solve for x. You now have your ratio scale 1:x.

Example: I measure the distance between two points to be 199,913.48 cm (image below). I will
round this number to 200,000 cm. The length of the line on the screenshot below is about 4 cm
(if you have printed this document or have it on a different size screen, the length may be
different).

4 cm / 200,000 cm = 1 cm / x cm
centimeters cancel out, yielding:

41

4 / 200,000 = 1 / x
4x = 1*200,000
x = 200,000 / 4
x = 50,000
The map scale is 1:50,000. On this scale, 1 cm represents 50,000 cm, 1 mile represents 50,000
miles, and 1 banana represents 50,000 bananas.

Figure 7-1. Topographic map of Blacksburg.

Geologic Maps
Geologic structures are identified in two ways: through the physical orientation of the rocks and
through the age relationships of the rocks in the region. Physical orientation of rocks is described
using strike and dip. Strike shows how the rock is aligned as an azimuth on the compass; without
a field compass, you may give a general direction (i.e., E-W, N-S, NW-SE). Dip is the angle of the
rock units to the plane of the horizon. The orientations of rocks relative to each other defines
geologic structures, which can affect the way the landscape changes over time and how materials
erode.

This symbol is a strike-dip symbol. You will see them on geologic maps to indicate the orientation
of the rocks. The long end runs parallel to the strike orientation, while the short end always points
in the direction of dip.

Here are some common symbols used in geologic maps (Federal Geographic Data Committee
Digital Cartographic Standard for Geologic Map Symbolization: Reston, Va., Federal Geographic Data
Committee Document Number FGDC-STD-013-2006 [prepared by the U.S. Geological Survey]). Not

42

all of these are in the Google Earth geologic map files, but you may encounter them later in your
careers.

Figure 7-2. General symbols used on a geologic map. Credit: FCDC, USGS

A syncline is a geologic feature in which rocks on either side of an axis dip towards the center of
the axis. A syncline will have an axis between two or more rock units, with the rocks on either side
dipping towards each other. The strike-dip symbols will be oriented so that the strike runs parallel
to the rock unit’s length, while the dip is towards the center of the axis. In Google Earth, it will be
easier to identify synclines by looking at the ages of the rocks: the youngest rocks will be in the
center, while the oldest rocks will be along the limbs. (You can remember that the rocks dip down
towards the syncline because synclines look like smiles and both start with S).

An anticline is the opposite of a syncline: the rocks on either side of the axis dip away from the
center of the axis. An anticline will have dip symbols on rock units that point away from the axis.
In an anticline, the rocks in the center will be older than the rocks in the limbs. (You can remember
that the rocks in an anticline look a little bit like an A).

A fault occurs where there is a break in rock units due to movement. There are three main types
of faults.

A strike-slip fault occurs when rocks move past each horizontally. Transform faults, such as the
San Andreas Fault, are a special type of strike-slip fault that occurs at plate boundaries. A road
built across a strike-slip fault will break and become offset on either side of the fault over time.
These faults are right-handed (if the road is offset to your right looking across the fault) or left-
handed (if the road is offset to your left looking across the fault).

A dip-slip fault occurs when rocks move up or down relative to each other. A thrust or reverse
fault is caused by compressional force, while a normal fault is caused by extensional force. These

43

rocks have what is called a hanging and a foot wall. The easiest way to distinguish these is to
draw a stick figure person over the fault line. The feet are on the footwall, and the head is on the
hanging wall (this is because miners used to hang their lanterns on the hanging wall). (See image
below). The motion of the hanging wall relative to the footwall is determined by correlating rock
units on either side of the fault.

Figure 7-3. Illustrations of normal and reverse/thrust faults.

One common cause of faults is due to plate tectonics. When continents collide, they produce
compressional force, which eventually overcomes the strength of the rock and forces it to break,
pushing the hanging wall up over the footwall. When continents rift, tensional force causes the
hanging wall to move down relative to the footwall.

Additional Resources:
https://serc.carleton.edu/serc/search.html?search_text=topographic%20maps&endpoint=%2Fse
rc%2Fsearch.html

Hanging wall

Footwall

Normal Fault Reverse and Thrust Faults

Footwall
Hanging wall

https://serc.carleton.edu/serc/search.html?search_text=topographic%20maps&endpoint=%2Fserc%2Fsearch.html

https://serc.carleton.edu/serc/search.html?search_text=topographic%20maps&endpoint=%2Fserc%2Fsearch.html

44

Assignment:
Download the Google Earth topographic and geologic map files for the state of Virginia and your
home state. Since we do not have files for international geologic maps, international students
should download the maps for Virginia and one other place they would like to visit in the US.
Topo Map
Geologic Maps of US states
Rocks from above

Topographic Map Activities:
1. Construct a ratio scale using the steps above. Please show your work for full credit.

(Remember, you can move around in Google Earth, but if you zoom in or out, your scale will
change!)

2. Center your map on the Brush Mountain (north-northeast of Blacksburg).
a. What is the highest elevation?

b. What is the average slope (m/km) on the NE side of the mountain? SW? Which is steeper?

c. In what direction does Poverty Creek flow? How can you tell?

d. What is the ratio scale for this particular map?

e. What is the magnetic declination of this area? Does a compass needle point east or west
of true north?

f. What is the contour interval on this map? What is the index contour interval?

g. Name one of the rivers/streams located within your map’s area. Which way is this stream
flowing, by compass direction?

h. The term “relief” is used to describe the difference between the highest and lowest
elevations in an area. What is the total relief in the quadrangle?

i. What do the small black (or purple) polygon symbols represent?

http://www.earthpoint.us/TopoMap.aspx

https://mrdata.usgs.gov/geology/state/

https://rocksfromabove.blogspot.com/p/google-earth-files.html

45

3. Contour the above plot to construct a topographic map

4. Now construct a topographic profile along the A-A’ line.
a. Lay a piece of scrap paper along the line of the section. Mark the two ends of the section

line.
b. At each point where a contour line crosses the section, make a small mark on your scrap

paper and label it with the elevation of the contour line.

46

c. Lay your scrap paper along the horizontal axis of the topographic profile (you may use
graph paper, but label your scale!). Transfer your contour intersection points and
elevations to this axis.

d. Using the contour value, plot a point at the correct elevation above each of your horizontal
axis marks, then connect these points with a smooth line to create the profile.

5. Now look at the New River between Radford and Pembroke.
a. Look at the terrain and elevation trends along the length of the river. Which part of the

river crosses the steepest terrain? Which part crosses the gentlest terrain?

b. Look at the shape of the river. How does the shape of the river channel and its valley
change along its length?

c. Calculate the gradient of the river over the entire length as well as between Radford and
Centerville, Centerville and Cowan, Cowan and Dry Branch, and Dry Branch and
Pembroke. Look at your numbers for the river’s gradient. Where does the river have the
steepest gradient? Where is its gradient gentlest?

d. Now draw a longitudinal profile. A longitudinal profile allows you to visualize the changing
gradient along a river’s length. A longitudinal profile is a graph of a river’s elevation versus
its length, and the slope of the profile is related to the segment gradient you calculated in
the previous section of the lab.

e. Get a piece of graph paper. Draw a line parallel to the long side of the paper, and make a
horizontal scale of one inch = 30,000 feet. Draw a second line parallel to the edge of the
short side of the paper, and make a vertical scale of 1 inch = 600 feet. (The highest number
on the scale should be larger than the elevation of the highest site along the river, and the
lowest number should be smaller than the elevation of the lowest site along the river.)

f. When the vertical and horizontal scales are not the same, a profile is said to have a vertical
exaggeration. To calculate vertical exaggeration, divide the vertical fractional scale by the
horizontal fractional scale:

i. The vertical scale is 1 inch = 600 ft. This equals 1 inch = ___________ inches. The
fractional scale is therefore 1/___________ (same number as above).

ii. The horizontal scale is 1 inch = 30,000 ft. This equals 1 inch = ___________ inches.
The fractional scale is therefore 1/___________ (same number as above).

iii. Vertical exaggeration = V scale/H scale = __________________________________

47

Geologic Map Activities:
Open the Geologic Map of Virginia Google Earth overlay file.

1. What Formation (by name) is found in Wolftown? ____________________________

2. What is its age? (Give the geologic Epoch.) ________________________

3. What Formation (by name) is found in Hood? ____________________________

4. What is its age? (Give the geologic Epoch.) ________________________

5. What Formation (by name) is found in Graves Mill? ____________________________

6. What is its age? (Give the geologic Epoch.) ________________________

7. Why do you think the rocks in this region appear in elongated strips? (Think back to laws such
as original horizontality, cross-cutting relationships, etc., and why rocks might change. Note
that the black lines on the map are faults).

8. Now look at the Culpeper region. What are the ages of the rocks around the area?

a. Do you notice any pattern in the distribution of the ages of the rocks around Culpeper?

b. What might cause the age distribution pattern of the rocks around Culpeper? Think about
the geologic history of the Eastern US involving continental collisions and rifting. (Check
with your TA to make sure you understand this feature!)

9. Now focus on the region between Elkton and Harrisonburg. Is this an anticline or a syncline?
How do you know?

a. Massanutten Mountain is the longest mountain in Virginia. Does it make sense that a
mountain is located here, given the structure you identified above? Why or why not?

b. How do you think the Massanutten Mountain was formed? (Pay attention to the rock types
under and surrounding the mountain and what you know about the rocks!)

48

10. Look at the area around Clintwood. Notice the pattern of the rocks. Do you think the rocks
here are flat, dipping East, or dipping West? Why do you think this?

11. Look at the geologic map located here: Geologic Map of the Pulaski Quadrangle, Virginia
a. Note that the key showing the rock units puts the oldest rocks at the bottom. This is a

convention with geologic maps. The file also has a geologic cross section from A to A’. A
geologic cross section shows a slice of the ground with the rock units shown as they are
oriented underground. The cross section provides useful information regarding the
geologic structures of a region, and can tell you how the ground is likely to erode and
how water will flow through the rocks based on the structure of the rocks.

b. Look at the fault on the right side of the cross section. Is this a normal or reverse fault?
How can you tell?

c. Now look at the fault on the left side of the cross section. Is this a normal or reverse
fault? How can you tell?

d. What is the structure to the left of the left hand fault? The structure on the right of the
fault? The structure on the left of the right hand fault? Do you think this sequence is a
common sequence?

https://www.dmme.virginia.gov/commercedocs/Pub_183

49

Appendix: A Quick Guide to Topographic Maps
All maps are two-dimensional representations of a three-dimensional world. A topographic map
shows you the shape of the land’s surface using contour lines that connect areas of equal
elevation. Most topographic maps also contain information about cultural features, such as roads
and buildings, and about vegetation, locations of streams, and other natural features. In the U.S.,
most topographic maps are made by the U.S. Geological Survey (USGS).

Important features of topo maps: Tools for map interpretation

Scale allows you to convert map distance into real-life distance. Map scales come in three forms:
A graphical scale is usually a line divided into segments showing what distance on the
ground is equivalent to a distance on the map.

Example: The map distance between the “0” tick mark and the “1000” tick mark on the
map represents 1000 feet on the ground.

A verbal scale states the number of feet or miles on the ground that equal one inch on the
map. It can be expressed in words or as an equation.

Example: 1 inch = 1000 feet
A distance of 1 inch on the map is equivalent to 1000 feet on the ground.

A fractional scale is a ratio of distance on the map to distance in the real world. It can be
expressed as a ratio or as a fraction.

Example: 1:12,000; 1/12,000
A distance of 1 inch on the map is equivalent to 12,000 inches on the ground.

Any combination of the three types of scales may be found on a map, so it is important to be
able to convert between them. A graphical scale can be converted to a verbal scale fairly
easily, by measuring the length of the graphical scale line. Converting a fractional scale to a
verbal scale is simply an exercise in unit conversion. All three examples above represent the
same map scale: 1:12,000, or one inch = 1000 feet.

Example: Converting fractional scale to verbal scale.

Q: For hiking, many people use 1:24,000 scale topographic maps. How many feet in the real
world are represented by one inch on the map?

A: The ratio 1:24,000 means that one inch on the map represents 24,000 inches in the real
world. This question is really just a unit conversion problem: how many feet is 24,000 inches?

1 foot = 12 inches
24,000 inches x 1 foot/12 inches = 24,000/12 feet = 2000 feet

So, on a 1:24,000 scale map, one inch on the map is equivalent to 2000 feet.

Contour lines: The elevation of the land surface above sea level is represented on a topographic
map by contour lines. Every point on a contour line has the same elevation. You can think of a
contour line as representing a horizontal slice through the land surface. A set of contour lines tells
you the shape of the land: hills are represented by concentric loops, whereas stream valleys are
represented by V-shapes in contour lines. Steep slopes have closely spaced contour lines, while
gentle slopes have very widely spaced contour lines.

50

The contour interval is the elevation difference between adjacent contour lines. It is important to
know the contour interval in order to interpret how steep a given slope really is, or how much
elevation difference is represented by a certain number of contour lines.

Every fifth contour line is an index contour, drawn darker than the other lines. If an index contour
is long enough, its elevation is usually written somewhere on it. If the contour interval is not stated
on your map, you can determine it from the elevation difference between adjacent index contours.

Map Symbols and Colors: USGS topographic maps use a standardized set of colors to
designate features:

• Black – man-made features such as roads, buildings, etc.
• Blue – water (lakes, rivers, streams, reservoirs, etc.)
• Brown – contour lines
• Green – vegetated areas such as forests
• White – areas with little or no vegetation
• Red – major highways; boundaries of public land areas
• Purple – features added to the map since the original survey

Coordinate Systems
Map-making faces the challenge of representing the Earth’s curved surface on a flat piece of
paper. Different methods called map projections are chosen based on the scale and purpose of
a particular map, but all projections result in some degree of distortion of the ‘ground truth’ being
mapped. Regardless of projection or distortion, all maps rely on a grid system to describe the
location of a point on the ground. There are several common grid systems (coordinate systems)
used on maps published in the U.S. All are based on a geometric X-Y coordinate system, where
X is the horizontal component and Y is the vertical component.

Geographic Coordinate System (GCS) – Latitude/Longitude: In the Geographic Coordinate
System, lines of latitude run parallel to the equator and divide the earth into 180 equal portions
from north to south. The reference latitude is the equator (0°), and each hemisphere is divided
into 90 degrees north and south. The north pole is 90°N and the south pole is 90°S. Wherever
you are on the earth’s surface, the distance between lines of latitude is the same (60 nautical
miles).

Lines of longitude run perpendicular to the equator and converge at the poles, and therefore do
not have an equal distance between lines at all points on the globe. The reference line for
longitude (0°) is the prime meridian, which runs from the North Pole to South Pole through
Greenwich, England. Longitude is subsequently measured from 0–180°E or W of the prime
meridian. Negative longitude values are assigned to lines west of the prime meridian.

GCS values can be stated in decimal degrees (Durango ex. -107.877, 37.287) or in degrees-
minutes-seconds (Durango ex. 107°52’32”W, 37°17’9”N). Each degree can be separated into 60
minutes (’) and each minute into 60 seconds (”). The USGS maps you will use in this lab are
called 7.5 minute quadrangles because each side of the map covers 7.5 minutes of latitude or
longitude.

51

Universal Transverse Mercator (UTM): The Universal Transverse Mercator system is widely
used because it produces the least amount of distortion for maps that cover large areas. In this
system, the earth is divided into 60 north-south zones that are each 6° longitude in width.
Coordinates are written as the UTM zone and an easting-northing pair in meters. The easting is
the projected distance in meters east or west of the center of the UTM zone. The northing is the
projected distance in meters from the equator (Durango ex. Zone 13, 244956, 4130253).

Public Land Survey System (PLSS): The Public Land Survey System is used mostly in the
western part of the U.S., originally to designate rural undeveloped areas. It is a grid system
measured in U.S. miles, with each township being a square of 6 miles on a side. Townships are
divided into 36 sections, each a square mile, and sections are divided into quarters and quarters
of quarters.

The red star in the diagram would be located as NW1/4, NW1/4, sec. 14, T2S, R3W.

• 1. Syllabus Information

Office Hours and Contact Information
Announcements
Assessment
Required Text (same as lecture)
Lab Structure
Honor Code
Disability Accommodation

• 2. Lab Schedule
• 3. Resources:
• 1. Plate Tectonics

Goals and learning objectives:
Reading:
Assignment:

• 2. Mineral Identification Lab

Goals and learning objectives:
Reading:
Why Minerals Matter
Additional Resources:
Mineral ID Charts:
Assignment:
Mineral Data Chart

• 3. Igneous Rock Lab

Goals and learning objectives:
Reading:
Additional Resources:
Assignment:
Igneous Rock Chart

• 4. Sedimentary Rocks

Goals and learning objectives:
Reading:
Components of Sedimentary Rocks
Assignment:
Sedimentary Rock Chart

• 5. Metamorphic Rocks

Goals and learning objectives:
Reading:
Components of Metamorphic Rocks
Metamorphic Rock ID Charts:
Assignment:
Metamorphic Rock Chart

• 6. Geologic Time

Goals and learning objectives:
Reading:
Assignment:
7. Maps and Structure
Goals and learning objectives:
Reading:
Materials needed:
Background Information:
Additional Resources:
Assignment:
Appendix: A Quick Guide to Topographic Maps

• 8. Earthquakes

Goals and learning objectives:
Reading:
Assignment:

• 9. Soils and Mass Wasting (?)

Goals and learning objectives:
Reading:
Assignment:

• 10. Groundwater

Goals and learning objectives:
Reading:
Calculating Groundwater Flow (SERC)
Assignment:

• 11. Rivers, Flooding, and Coasts

Goals and learning objectives:
Reading:
Additional Resources:
Assignment:

GEOLoGIC TIME ScALE
LiFE GEOLOGIc EON ERA PERIOD EroCH DATES EVENTS WESTEVENTS EASZ

QuarternaryPleistocene
Pliocene
Miocene
OWgocene
Eocene

9Neo0
gene 23.8 Tertiary

Paleo-
gene Paleocene 65 m ExTINCTION
Gretaceous

L 142 m Jurassic 205.7 mexTINCTION Alantic opening
Pangea breakup

1St

TriassicC TMammals Thecodont repues Mammall 248.2 mTINCTION
Aes Permian ep First

repiies 290 m Glacia
tion Coal Pennsylvaniane

Mississippian|
323 m

Crinoid Amphib

meadows ans 354 m ErTINCTION Tabulate Fish Stro commo ree Devonian
Silurian

-ordovician
Cambrian

417 m
New Inyert.) and

radiation plants 443 m exTINCTION Gondwana
glaciation Invertebrate adaptive

radiarion Trilobites common 495 m
Cambrian invert.

radiation
Ediacaran fauna
first soft bodied

animals)

545 mTommatian stage Glacia lapetan openins Kendian stage
hiphean stage ton

Late
9

Bitrer Springs
fauna

Siberia/
NA i

apan
Middle

1.6b
Gunflint fauna

Oides
probable
eukaryoles
Stromatolites

are abundant

Early
2.5 b

Barberton Fig Tree fauna
Onverwacht fauna
Warawoona fauna

Greenstone
Earth Belt S. Africa

covered
With (oldest fossils)
any

micro
contipenis

3960 m oldest rocks
4.6 b irst

continent crust
L.S. Fichter, 19977

123

Stratigraphy of the Central and Northern
Shenandoah Valley, and Eastern West Virginia
SequenceAGEWest FORMATIONEast Thickt DESCRIPTION Interptetation

MAUCH CHUNK
R GREENBRIAR

PocONO

Coarse s, silt, shole. Channels. Plant fossils

common in places, Coal_
Carbonate dominated (oolites, biosparites)

Begin Alleghenian
Orogeny

Orogenic Calm

300- Quartz sandstone & conglomerate; coarse,
1700 thick, large cross beds

HAMPSHIRE
GREENLAND GaP
iROUP (former Chemumg). FoREKNOBS

BRALLIER

(Catskill) 2000 Point Bar Sequences; red

Thick hummocky sequences; at top interbed-
ded red and green fine sonds and silts 2000 SCHEER

1500-
(Portage in Pa.) 1700 Bouma

sequences

MILLBORO
(Used south of
Shenandoah Co.)

lully
Harrel
Mahantango 900|

Dark gray to black silts and fine sands

Marcellus 350-500
100-

530 fossils abundant in places
Olive groy fine sands, silts, and shales; NEEDMORE

M Wallbridge Uncontormity
ORISKANY

Tioga bentonite

10- Quortz arenite; white, gray, Tan;
125 abundant fossils

LICKING CREEK
MANDATA
NEw ScoLAND70-150 cherts, or interbedded with shale or quartz

NEw CREEK 17-50| arenites; fossils very abundont
KEYSER

HeLDERBERG Corbonates of many kinds; sometimes with
GROUP

70-6001
50-2501 dal carbonates; ALM, ALD; mud cracks; TONOLOWAY (Salina in Wa.)

WILLS CREEK
WILLIAMSPORT

McKENZIE

salt costs; evaporitic to west
BLoOMSBURG 0-400| Bloomsburg: red very fine sonds/sils/shale

0-75 Yllow.calcareous shale: fossils
KEEFER

RoSE HILL
TusCARORA

|70|Massanutfen: coarse friable quartz orenites
and conglomerates with large planar X-beds

bOU Tuscarora/Keefer: quartz arenites; ripples
50- Skolithus. Rose Hill: red fine – coarse sands

and shales; loads, ripples, frace fossils
Gray

Swhite, coarse
X-bedded sands

MASSA- 5
NUTTEN

250

JuNIATA L20-200 Red X-bedded s, Skolithus; bedded
OsWEGO Cub Hum- SS”O-375| W/Sh_

Clastic hummocky
mocky

REEDSVILLE
TRENTON
GROUP

Feldspathilithie
Bouma sequences

Ggoy sily’shale_

MARTINSBURG 3000sequences
Carbonate

Oranda 40-60| hummocky
?

-BLACK RIVER
GROUP”

Liberty Hall)
EDINBURG 600 Lantz Mils

Black massive
micrites and shale

425-Equences_

Carbonate hummocky

SMicrites, bio- and
pelmicrites, chert

sequences

25-170
LINcoLNSHIR�

NEW MARKET
40-250 bundant fossils, darkens up section_

Very pure micrites; tidal features
Knox Unconformity

BEEKMANTOWN (Rockdale Run)
STONEHENGE (Chepultepec)
CoNOcOCHEAGUE
ELBROOK
ROME Waynesboro)

E SHADY

2500 | Thick bedded dolomite, black chert; tidal
500 Thick bedded micrite, blve; tidal features

2500 LS/dolo/qtz arenite ; abndt tidol structures
2000 LS/dolo/ blue-gray; tidal feotures
2000 Red/green shale/dolo/micrte, very voriable
1600 Dolomite (granular); LS at top and bottom
500- Qugrtz arenite; abndt X-beds

1500 Skolihus O ANTIETAM

B WEVERTON
Thin bedded

shale and graded sandstones HARPERS 2000 Cs feldspathic
800 large planar

X-beds
and Bouma sequiencAs

ICATOCTIN 1ALFEIRERB IIFNE 2000 Subareal tholeiti, fod basals ( ow greerschir)
SwIFT RUN
GRENVILLE BasEMENT

LYNCHBURG)
East of Blue Ridge

L.S.Fichter, 1991 (reformatted 1996)