Mont Blanc's mountain range (4)
I believe the answer is:
alps
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">mont blanc's mountain range</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for alps that I've seen before include "Eur. mountain range" , "South-central European mountain system" , "Peaks" , "Mountain system in south-central Europe" , "Mont Blanc is therein" .)