logan stone
Concise Oxford English Dictionary © 2008 Oxford University Press:
logan stone /ˈlɒg(ə)n, ˈləʊg(ə)n/
▶noun a boulder poised in such a way that it can be easily rocked.
– origin C18: from logging (from dial. log ‘to rock’).
'logan stone' also found in these Oxford entries:

