The aphorism "Don't wase words Jump to Conclusions!" is, without fail, attributed to Millican Dalton. However there is only annecdotal evidence it was written by him or that he ever used it.

DON'T !!       
WASTE WORRDS
Jump to            
                 Conclusions            
                              MD

Notes:
1) The two parts are carved in different styles.
2) The second R in WORRDS appears to have been added later
3) The MD does not appear as deliberate as the rest - it may have been added later.

The evidence:
• The aphorism is carved into the wall of Attic Cave and signed MD.
• Matthew Entwistle's book offers annecdotal evidence that the first part was carved by an unidentified scottish friend of MD and that MD carved the second part as a response. Entwistle ascribes the the double "R" letter to the rolling R of Scots.
• We know that MD was renouned for being argumentative, stubborn and for simple living - so the phrase fits him well.

In conclusion:
The words may possibly not have been his original work, but in the absence of any evidence one way or the other we have to assume that Millican Dalton executed the carving and stood by the words.