The forest was dark and the trees too many. I could hardly tell shadows apart.
Is the usage of apart correct in the passage above?
(I'm wondering about this because a Google Books search returned only one result).
There isn't anything inherently ungrammatical about your example but it is slightly confusing:
Apart from what? Other shadows? Trying to tell shadows apart from other shadows is always difficult. Any alternatives would depend on the specific context but it may help to clarify the sentence.