Strike of quartzite bed dipping S25°E

The strike is always at 90° to the dip direction.

Given: dip direction = S25°E, which is azimuth $180° - 25° = 155°$.

$$\begin{aligned} \text{Strike azimuth} &= 155° - 90° = 65° \\ \text{(or } 155° + 90° &= 245° \text{)} \end{aligned}$$

So the strike is N65°E (the same line is S65°W).

               N
               |        strike N65E
               |     /
               |   / 65
        W -----+-/---------- E
               | \
               |  \ 25
               |   v  dip direction S25E
               S

The strike line and dip direction are perpendicular: the strike is 25° north of east and the dip direction is 65° south of east (25° + 65° = 90°).

Answer: Strike = N65°E (S65°W). For the sandstone bed with the same dip direction in the net-diagram version, mark the strike N65°E-S65°W as a diameter of the stereonet. The great circle of the bed joins the two strike ends and bows towards S25°E (the dip direction); its pole plots on the opposite side, along N25°W. The dip amount fixes how far the great circle bows in from the primitive circle.