Geological Structures Questions and Answers

Answer: A

Correct answer: both the assertion and the reason are true and the reason explains the assertion

Both are true and the reason gives the mechanism. Where a bed dips, its outcrop stands at a lower position in the valley floor than on the interfluves on either side, so the trace swings up the valley and closes to an apex pointing down dip. The rule fails only where the dip is gentler than the stream gradient, in which case the V reverses.

Answer: B

Level ground cuts a vertical bed at right angles, and only then do width and thickness coincide. For any other dip the width is the thickness divided by the sine of the dip, so it exceeds the thickness sometimes greatly.

Answer: C

Correct answer: the elevation of a bedding surface

Structural contours describe the shape and depth of a surface; isopachytes describe how thick a formation is. The two are independent - a bed can thicken while it descends, or thin while it descends - and answering a question about depth with a thickness map is a common confusion.

Answer: D

Correct answer: its strike together with its dip

A plane in space needs two quantities to fix its orientation, and strike and dip are the pair conventionally used. Either alone leaves a whole family of possible attitudes, and outcrop width fixes neither, depending as it does on the thickness and the dip together.