*4.5. Analysis of Boulder Shapes*

Raw data on boulder size in three dimensions collected from each of four transects across the Almeja CBB are available in Appendix A (Tables A1–A4). Points representing individual blocks grouped by transect are plotted on a set of Sneed-Folk triangular diagrams (Figure 7a–d), showing the actual variation in shapes.

Those points clustered closest to the center of the diagram are most faithful to an intermediate value. With only rare occurrences registered, the absence of points at the top of the triangle signifies that no boulders eroded from equidimensional cubes are present in the sample. Also, the lack of points in the lower, left tier of the triangle demonstrates that squarely plate-shaped blocks are completely absent from the assemblies. Overall, the points grouped from different transects trace similar trends in direction from the center to the lower right tier of the diagram. The recurrent relationship denotes the presence of subpopulations of elongated boulders in the shape of shoe boxes. The significance of such diagrams puts a heavy emphasis on the thickness of parent rhyolite flows and the spacing of intersecting vertical joints in the bedrock (Figure 4). This result has a direct bearing on the relative ease with which individual blocks might be pried loose from the bedrock by wave action and fall into the sea. The process of rounding is expected to occur from the grinding of blocks against one another under wave surge against the headland. Although the trends in shape are similar among the samples from different transects (Figure 7), the plots have no bearing on variations in boulder size.

**Figure 7.** Set of triangular Sneed-Folk diagrams used to appraise variations in boulder shape; (**a**) Trend for boulders from Transect 1; (**b**) Trend for boulders from Transect 2; (**c**) Trend for boulders from Transect 3; (**d**) Trend for boulders from Transect 4. Note: All trends slope to the lower right, indicating shapes conserved by elongated boulders.
