Geology Reference
In-Depth Information
h.
Approximate area covered by the map (in both mi
2
and
km
2
)?
PART B. GEOLOGIC MAPS
Geologic maps show the distribution of rock units at
the earth's surface, as though the regolith (loose
unconsolidated materials) were stripped from the
bedrock. The basic rock unit mapped is the geologic
formation. Some geologic maps combine formations
and show only units that include all rocks of a given
age. Soil and regolith are shown as map units only
when they are unusually thick or are directly associ-
ated with recent geologic processes, such as floodplain
and landslide deposits, or glacial drift. In addition to
earth materials, faults and other geologic structures
are shown on geologic maps and the relative age of
these materials and their arrangement beneath the sur-
face are indicated.
By convention, formations are identified on geo-
logic maps by color or pattern (see Figure 2.10, in map
section at the back of the topic), and are labeled with a
letter abbreviation, which gives the geological age or
name of the formation. Usually the color or pattern
and the letter symbols for all ages and formations used
on a map are printed in an explanation along the map
margin. The oldest formation is listed at the bottom. In
addition to color, line, and letter symbols for forma-
tions, geologic maps may also contain a wide variety
of other symbols, depicting rock structure (strike and
dip), economic rock or mineral deposits, and other
geologic features.
A good geologic map contains a great amount of
information. When used in conjunction with topo-
graphic maps or aerial photographs, they can provide
much of the basic information needed for studies con-
nected with mineral and mineral fuel exploration, con-
struction projects, urban planning, and surface and
subsurface water problems. They also tell us much
about the geologic history of an area.
Study the geologic map of central North America
Figure 2.10 (in the maps section) to help answer the
questions on geologic maps below.
i.
Latitude and longitude of the northeast, northwest,
southeast, and southwest corners of the map?
(NE)
(NW)
(SE)
(SW)
j. Names of quadrangles located north, east, south, west,
northeast, southeast, southwest, and northwest of this
quadrangle?
k.
Note the variety of symbols used on the map. Find exam-
ples of each of the following and give its location by either
latitude and longitude coordinates or by township, range,
section, and quarter-section locations. Also note the rela-
tionship to major features or to the general area covered.
A bench mark.
A spot elevation other than a bench mark.
A school or church.
Features shown in:
QUESTIONS 2, PART B
blue:
1.
Using Table 2.1, the explanation for Figure 2.10, give the
words for the following symbols:
brown:
p-€ m
black:
Di
red:
K
green:
2.
What is the age in millions of years of the boundary
between the Cambrian and the Precambrian (Hint: Consult
the geologic time scale in Appendix II)?
