What is that, rotting leaves?

It has technically been Autumn for a while now, but today...today it was Fall.  There was a chill in the air that only happens in Fall, and a breeze that shook the leaves out of the trees.  I walked out of my office building at the noon hour today and the smell of Fall just hit me...what is it exactly?  Slowly rotting leaves and plants in the garden beds?  Maybe, but it smelled wonderful!  This week the leaves actually starting turning color, and my favorite time of the season is when they have mostly turned but have not yet all fallen, so that is something I will look forward to.