Which one of the following relationships between the topographic contour value (t) and the stratum contour value (x) of a bed must be TRUE for an outcrop of the bed to occur on the topographic surface?
- t = x
- t = 2x
- t = 3x
- t = 4x
The Correct Option is A
Solution and Explanation
To determine the correct relationship between the topographic contour value (\( t \)) and the stratum contour value (\( x \)) for an outcrop to occur on the topographic surface, we need to understand the concept of outcrops and contours.
Explanation:
An outcrop refers to a situation where a geological formation appears on the surface of the Earth. For an outcrop to occur, the elevation of the layer of rock or stratum (stratum contour value, \( x \)) must match the elevation of the Earth's surface (topographic contour value, \( t \)).
The relationship can be understood as follows:
- Topographic contour (\( t \)): A line on a map representing points of equal elevation on the Earth's surface.
- Stratum contour (\( x \)): A line indicating the elevation of a particular geological layer.
For the rock layer to appear on the surface (i.e., outcrop), the elevation of the top of the stratum must equal the elevation of the land surface. This means that the topographic contour value (\( t \)) must equal the stratum contour value (\( x \)).
Correct Answer: t = x
Let's evaluate other options:
- t = 2x: This suggests that the topographic surface is twice the elevation of the stratum, which does not allow for an outcrop.
- t = 3x: This implies an even greater disparity in elevation, making it impossible for the layer to surface.
- t = 4x: Similar to the previous options, this relation indicates a significant elevation difference, preventing an outcrop.
Hence, the only condition where the bed can outcrop at the surface is when t = x, making it the right choice.
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