Substance is related to Stone. Stone is related to Heavy. Heavy is similar to Steep. 
Surface is related to Forehead. Forehead is related to Eye. Eye is related to Obstacle. 
Substance <--RelatedTo--> Stone <--RelatedTo--> Heavy <--SimilarTo--> Steep 
Surface <--RelatedTo--> Forehead <--RelatedTo--> Eye <--RelatedTo--> Obstacle 