The measurements of the outcrops reveal that in the upper
catchment of the Peinan River, the volumetric joint count, Jv, in the
Pilushan Formation ranges from 27.6 m−3 to 47.6 m−3 with an
average of 35.8±6.7 m−3; the Jv value in the Marble ranges from
6.2 m−3 to 8.1 m−3 with an average of 7.0±0.5 m−3; the Jv value in
the Black Schist ranges from 16.0 m−3 to 46.6 m−3 with an average of
32.6±5.5 m−3; and the Jv value in the Mixed Schist ranges from
26.2 m−3 to 61.3 m−3 with an average of 47.3±3.4 m−3. According
to the classification scheme of the International Society of Rock
Mechanics (Brown, 1981), the block size of geomaterial in the
Pilushan Formation, Black Schist, and Mixed Schist belongs to the
“small block” or “very small block” group, and the block size of
geomaterial in the Marble belongs to the “medium-sized block”
group.