Depth of field. It can’t be contrast because there is nothing different between the two sides. They are mirror images that are powerful because of the vast mass of trees.
For most part of his life William Blake was not recognized as the great artist he is considered today, and it was mainly because of the lack of technology to print his engravings. He is considered as the Complete British Artist, he was a poet, a painter and an engraver, so his work needed to be seen from three angles to be fully understood.
The answer to this question is his engravings.
