Table of Contents
What is legend in geological map?
Legend is a table explaining the meanings of all colours and symbols used to represent geologic features in the geological map, cross section and litostratigraphic column.
What is a symbol in geological map?
The letters indicate the rock formations, with the first letter being the geologic period. The remaining lower case letters abbreviate the formation name, which includes a geographic name where you could go to see the rocks. The formations on this map include: Qal, Quaternary alluvium.
In what order are rock units usually arranged in a legend?
Legend – the legend is a key to the patterns used to identify each unit on the cross-section. The units are ordered from oldest formation at the bottom of the legend to youngest unit at the top of the legend.
Why is a legend important on a map?
The map legend contains all the symbols (symbology) used in the map to help the reader understand what the polygons, lines, points, or grid cells represent.
What are the two main types of contacts shown on a geological map?
Contact and fault lines. The two main types of contacts are depositional contacts and faults. Depositional contacts are created when geologic units are composed under, over, or next to each other.
What do the numbers next to the dip symbols represent?
The number represents the plunge, or the dip angle in that direction.
How do you identify faults on a geologic map?
Faults are marked on geologic maps with bold lines. These lines are broader than the lines used to mark contacts between rock units.
What is dip azimuth?
Dip azimuth is the direction (relative to north) that plane is dipping, where values range from 0 to 360. Specifically, dip magnitude and azimuth are calculated from the apparent dips of inlines and crosslines.
What is the oldest rock unit?
The oldest geologic units in the study area are the Precambrian crystalline (metamorphic and igneous) rocks (fig. 2), which form a basement under the Paleo- zoic, Mesozoic, and Cenozoic rocks and sediments.
What can a map legend tell you?
A map legend or key is a visual explanation of the symbols used on the map. It typically includes a sample of each symbol (point, line, or area), and a short description of what the symbol means.
What is an intrusive contact?
Intrusive contacts are the surfaces between host (or country) rock and an intrusive magmatic body. The older country rock is crosscut by a younger magmatic body. The nature of the intruding body depends its composition and depth. Common examples are igneous dikes, sills, plutons, and batholiths.
How do you read strike and dip on a map?
Strike and dip map symbols look like the capital letter T, with a short trunk and extra-wide top line. The short trunk represents the dip and the top line represents the strike. Dip is the angle that a bed or layer plunges into the Earth from the horizontal. A number next to the symbol represents dip angle.
What is the right hand rule in geology?
Right-Hand rule: rather than reading the strike to a north quadrant (NE: 0-90; NW: 270-360) the strike trend is recorded in the azimuth direction such that the true dip (incline) of the plane is to the observers right. This removes the need for a quadrant direction for the dip.