 Work on the foundations for the lighthouse continued until 30 September . A total of 296 charges were used to remove 2 @,@ 000 tons of rock and Stevenson believed that the rock was so hard that the effort involved was four times that required for boring Aberdeenshire granite . The work went well but by the end of the second season , no blocks had yet been laid . However , between April 1839 and June 1840 4 @,@ 300 blocks had been fashioned , the stone donated by the Duke of Argyll from quarries on Mull . The roughly hewn rock was taken to Hynish where the blocks were hammered and chiselled into shape . The largest weighed over 2 @.@ 5 tons , the smallest 0 @.@ 75 tons and the precision required meant that a single block could take 320 man hours to complete . 
