Strike of limestone bedrock dipping N31°W

The strike is the direction of the horizontal line on the bed and it is always at 90° to the dip direction.

Given: Limestone bedrock dips towards N31°W. Dip direction = N31°W, azimuth = 329°.

$$\begin{aligned} \text{Strike} &= \text{dip direction} \pm 90° \\ &= 329° - 90° = 239° \ \text{or}\ 329° + 90° = 59° \end{aligned}$$

These two azimuths (59° and 239°) are the two ends of one line, so the strike is N59°E (S59°W).

                    N
     dip N31W \     |     / N59E
                \   |   /
                  \ | /
  W ----------------+--------------------- E
                  / |
                /   |
         S59W /     |
                    S
   ( / = strike line N59E-S59W,  \ = dip direction N31W, at 90 deg to strike )

Answer: Strike = N59°E (S59°W).