Screaming or howling in Surry County, Virginia

My family and I were trying to get some sleep in our tent on this particular evening (invariably, we always seem to somehow end up next to a bunch of noisy and inconsiderate campers who keep us up until the wee hours of the morning!) However, in this particular case, I was glad to have had other camping company around. The noisy campers in question had finally settled in for the night (or should I say, early morning)and it wasn't long after quiet settled in, about fifteen minutes or so, that I heard a very, very strange and unfamiliar howling off in the distance. It seemed to come from about a distance of a half mile or so from the general direction of the James River.The sound, or howl, had a deep resonating tone that I can only describe as a blend between a mournful human yell and a high piercing screech, which started in a low pitch and quickly pulsed to a higher pitch. Each one of these howling events lasted about 10-20 seconds, they varied from 3 to 10 minutes apart and were different in intensity and, seemingly, location and distance. Two of the howls appeared to be getting closer, as the noise level and intensity increased on these occasions. The whole thing lasted about 30 minutes and I only heard these howls about 5 times within that half hour or so, and then the last thing I remember was falling asleep into the silence of the morning after the howls disappeared. Our Chesapeake Bay Retriever did "grumble-bark" upon hearing each of these howls, but did not behave in any unusual way.The only thing I can say is that after all the time my father, brother and I had spent in the woods of Oregon and in the Sierra-Nevada's in California, I have never heard anything like the noises I heard that night. The rest of my family was asleep, which made this whole thing even more erie for me since I did not have my wife's ever-present wisdom and practicality to balance out what I think I had heard. Make no mistake about it--I slid three shotgun shells into my 12-guage that night and slept uneasily for the rest of the morning, clutching my gun tightly and staying accutely aware of any behavioral changes in Chester (my Chesapeake Bay Retriever).