Fitting, Fretting and Imprisoned Boulders

Abstract

THE occurrence on rocky coasts of what Shelley¹ aptly calls “fitting boulders” is, as he says, not mentioned in standard works on shore processes; but the late Professor J. A. Bartrum discussed such boulders with me in 1934 and used the term “fretting” in relation to the development of common interfaces between adjacent boulders. Baker² described an example near Cape Paterson in Victoria (Australia) using the term “imprisoned rocks”, and indeed they are not uncommon on the Victorian coast. I have observed them at Beaumaris among blocks of soft red Tertiary sandstone derived from collapses of the cliff face, also at Sorrento in Pleistocene calcareous aeolianite, and again around Lorne and Cape Paterson where the rocks are Mesozoic arkoses. They occur also at St David's (South Wales). Shelley's descriptions afford a basis for comparison.