MEHRAN UNIVERSITY OF ENGINEERING
AND TECHNOLOGY
ENGINEERING GEOLOGY PRACTICAL
NO:3
TOPIC: THE STUDY OF GEOLOGICAL
MAPS.
NAME: HUZAIFA ALI
ROLL NO: 18CE193
SUBMITTED TO: SIR AMMAR NOOR
MEMON
1) GEOLOGICAL MAPS CONCEPTH:
Geological or geologic maps are not like other maps.geological maps are desighned to show where
things are.It shows the distribution of road,river ,country and boundary also.it shows the geological
feature including kinds of rocks and faults,soil.geological map is usually printed on top of a regular
map(called a base map) to help yourseld locating.Geological maps are represented by colours which is
its striking textures.Geological unit is a volume of certain kinds of rocks of a given age range. Geologic
maps are important for two reasons. First, as geologists make geologic maps and related explanations
and cross-sections, they develop a theoretical understanding of the geology and geologic history of a
given area.Second, geologic maps are essential tools for practical applications such as zoning, civil
engineering, and hazard assessment.
2) SIGNIFICANCE OF COLOURED AREAS ON GEOLOGICAL MAPS:
The use of color in maps and data visualizations has a long tradition. Color, along with position, size,
shape, value, orientation, and texture is one of the primary means to encode data graphically. Many
colors used on maps have a relationship to the object or feature on the ground. For example, blue is
almost always the color chosen for water.
3) LETTER SYMBOLS:
Each geologic unit is assigned a combination of an initial Capital letters followed by one or more small
letters.
1) CAPITAL LETTERS:
The capital letter represents the age of the geologic unit,Eons,Eras,Periods and Epochs,bassed on the
fossils found in rocks.If the rock unit contains more thn one time unit two capitals letters are used.QT-
would indicate that rock unit began to form in tertiary time and was completed in quaternary time.If the
age is un known,No capital letters are used.J,K,T,Q letters show period.
2) SMALL LETTERS:
Small letters define the name of the unit or the type of the rock like:
Kjm-Joaquin miller sandstone formed in the cretaceous period.
Ks-unnamed unit of shale formed in the cretaceous period.
Gb-gabbro(a dark coloured igneous rock) of unknown age.
4) LINES ON THE MAP:
1) CONTACT LINES:
The place where two different geological units are found next to each other is called contact.It is
represented by different kinds of lines on geological map. The two main types of contacts shown on
most geologic maps are depositional contacts and faults.
1) DEPOSITIONAL CONTACT:
All geologic units are formed over, under, or beside other geologic units. For example, lava from a
volcano flows over the landscape, and when the lava hardens into rock, the place where the lava-rock
rests on the rocks underneath is a depositional contact. Where the original depositional contact
between geologic units is preserved, it is shown on the geologic map as a thin line (location 4).It is
shown as a thin line.
2) FAULT LINES:
When different geologic units have been moved next to one another after they were formed, the
contact is a fault contact, which is shown on the map by a thick line (location 5). Faults can cut through a
single geologic unit. These faults are shown with the same thick line on the map, but have the same
geologic unit on both sides.
2)FOLDS:
Another kind of line shown on most geologic maps is a fold axis. In addition to being moved by faults,
geologic units can also be bent and warped by the same forces into rounded wavelike shapes
called folds. A line that follows the crest or trough of the fold is called the fold axis. This is marked on a
geologic map with a line a little thicker than a depositional contact, but thinner than a fault (location 6).
3) SOLID DASHED OR DOTTED LINES:
All thicknesses of lines are also modified by being solid, dashed, or dotted. Often contacts are obscured
by soil, vegetation, or human construction. Those places where the line is precisely located it is shown as
solid, but where it is uncertain it is dashed (location 7). The shorter the dash, the more uncertain the
location. A dotted line is the most uncertain of all, because it is covered by a geologic unit, so no amount
of searching at the surface could ever locate it (location 8). The lines on the map may also be modified
by other symbols on the line (triangles, small tic marks, arrows, and more) which give more information
about the line. For example, faults with triangles on them (location 9) show that the side with the
triangles has been thrust up and over the side without the triangles (that kind of fault is called a reverse
fault or a thrust fault).
4) STRIKE AND DIP:
Tilted beds are shown on geological maps by strike and dip.Its symbol consist of three parts:Long
line,Shhort line and a number.The long line is called the strike line and shows the direction in the
bed.The strike line shows the horizontal direction.Short line is called the dip line,shows which way the
bed is tilted.The number shows how it is tilted in degrees from flatis called dip.
5) MAP KEY:
All geologic maps come with a table called a map key. In the map key, all the colors and symbols
are shown and explained. The map key usually starts with a list showing the color and letter
symbol of every geologic unit, starting with the youngest or most recently formed units (in the
example map those are the man-made deposits), along with the name of the unit (if it has one)
and a short description of the kinds of rocks in that unit and their age (in the key, the age is
described by Epochs, subdivisions of the Periods shown in the letter symbol). After the list of
geologic units, all the different types of lines on the map are explained, and then all the different
strike and dip symbols. The map key will also include explanations of any other kinds of geologic
symbols used on a map (locations where fossils were found, locations of deposits of precious
metals, location of faults known to be active, and any other geologic feature that might be
important in the area shown by the geologic map). Because the geology in every area is
different, the map key is vital to understanding the geologic map.
