Complex sentence: Typically the uppermost rock has been transported and deposited by the very slow action of a glacier; the lower part of the rock formation might or might not have also undergone a degree of erosion to accentuate the mushroom shape.
Split into simpler sentences: Typically the uppermost rock was transported and deposited by the slow action of a glacier. The lower part of the rock formation might or might not have also undergone a degree of erosion to accentuate the mushroom shape.