 The island 's relief is spectacular , a 19th @-@ century commentator remarking that " the interior is one heap of rude mountains , scarcely possessing an acre of level land " . This combination of geology and topography make for less than ideal agricultural conditions , and it is doubtful that more than one tenth of the island has ever been cultivated . In the 18th century average land rental values on Rùm were a third those of neighbouring Eigg , and only a fifth of Canna 's . 
