In this paper, we quantitatively demonstrate that dominant erosion processes on different shore platforms can be explained, in part, by geological properties. We selected sites with a considerable history of rock coast geomorphology study, to evaluate whether geological data can improve our understanding of spatial variations in erosion between sites. Schmidt Hammer tests and discontinuity data were collected on Blue Lias limestone shore platforms in Wales, UK, and sandstone platforms in Victoria, Australia. Significant differences in joint spacing, persistence of discontinuities and block size were found between the Australian and Welsh study sites. These data were related to evidence of meso-scale erosion to examine how geological contingency influences the nature and scale of erosion processes and thresholds. This study quantitatively demonstrates that discontinuities play a fundamental role in altering rock resistance. The findings of this research have important implications for the design of rock coast erosion studies concerned with measuring rates of change and determining the relative contributions of different processes to platform development.