A mountain shape is a large standing piece of wax that stands up freely as the candle burns down. These will sometimes melt down over the course of the work, but will sometime remain even after the work has burned out.
These formations symbolize something negative that is holding on or blocking the work. They typically represent obstacles that are somehow inherent in the situation and standing between you and your target or goal.
Look at the position of the mountain to tell where the blockage is located in the work.
What to Do:
The best way to handle mountains overall is to dress another candle or a match with a clearing or cleansing oil and use it to melt down the hook. This loosens and removes the obstacle. Pray specifically to your spirits to help remove the blockage in the way most consistent with your well being and goal.
You may also need to do work specifically to fix the blockage indicated by the mountain. For exmple: a love work that shows a mountain to the lower right may be showing that the spell is being blocked by financial troubles for the target. Money work may be a good way to fix this specific problem so that the love spell can move faster.