There are several possible reasons for black stools. Some of them are as simple as taking iron supplements or Pepto Bismol or even eating licorice, but it can also be a sign of digested blood, which means the blood would have come from higher up your gastrointestinal tract than just your rectum and anus.
http://www.wrongdiagnosis.com/symptoms/black_stool/causes.htm
I'm glad you are going for a physical in November, but maybe you want to call your doctor sooner, just in case it's something serious.
I appreciate the link and I love Wrong Diagnosis for being so well indexed, but I was using the term "blackjack" more to describe the size and shape rather than the color, in that it was much larger on one end. The blood was very fresh and, I'm sure, the result of the shear size and inflexibility of that particular stool.
The color was about normal, considering the quantity of vegetables I have had recently. I would call it on the dark side and iron heavy, but nothing like black. I really believe that I have gotten my vegetable to fruit balance off by quite a bit, this week. The odd thing to me is that I have only recently begun to have any concerns about "that end" of my diet. As I mentioned earlier, my first encounter with constipation was about two months ago. I now have a bit more sympathy for those who deal with it on a daily basis, like my daughter and my wife.
I had a mild peptic ulcer when I was in my thirties and I remember distinctly the smell of blood in my breath and my stool. This was not the same at all. If it happens again, I will definitely call the doctor, though. I know there are prescription stool softeners that worked miracles during the time my wife was having her worst difficulties with constipation. Pregnancy messed her up "real bad." She was pregnant a lot, over a long period of time, even though we only have two kids to show for her miseries.