True thickness from apparent thickness 210 m

Principle: in a vertical borehole the thickness measured is the vertical (apparent) thickness $t_v$. The true thickness (perpendicular to the bedding) is smaller for a dipping bed:

$$t = t_v\cos\delta$$

Given

$t_v = 210$ m, dip $\delta = 36^\circ$ (attitude 220°/36° NE).

Calculation

$$\begin{aligned} t &= 210\cos 36^\circ \\ &= 210 \times 0.8090 \\ &= 169.89\ \text{m} \end{aligned}$$

        borehole
          |
     _____|______  top of bed
    |     | tv   /
    |     |    /  t (true)
    |_____|__/__  bottom of bed
          |/ dip 36 deg

Answer: true thickness of the quartzite = 169.9 m.