I was on Continental flight 1500 out of Ft Lauderdale enroute to Newark ,NJ , at 4:30 ( I checked the time) I observed a very Black dot against the white clouds out the right side of the aircraft. I estimated several miles away - visibility was good 35000 ft. It seemed like a smoke cloud getting slowly larger and then looked like the shape of a long triangle sitting still, then flattened out and looked like a line of black going opposite our direction. I tried some digital pictures but only got a fuzzy black line. I thought possibly military? But I have never seen the very black trail before. We were above the clouds, probably not seen from the ground / ocean. I did speak to the pilot, who stated he did not see it. I am curious as to what it was or if anyone else saw it.