had lost his regulator and did not seem to be making any attempt to replace it. She drew up beside him and flashed the thumbs-up sign. There was no response. Nick's eyes were closed.
Carol felt a surge of adrenaline as she reached for Nick's regulator and thrust it into his mouth. She beat against his mask with her fist. After a few painfully long seconds, Nick opened his eyes. Carol tried thumbs up again. Nick shook his head, as if he were clearing out the cobwebs, smiled, and then returned the okay signal. He started to move but Carol restrained him. She indicated with gestures for him to sit still while she hurriedly looked him over. From the force with which Nick had hit the reef, Carol feared the worst. Even if his diving gear was all right, certainly his skin would have been ripped and torn by the sharp coral and the impact. But incredibly, there did not appear to be significant damage to either Nick or the equipment. All she could find were a couple of small scrapes.
The three whales remained in the same area where they had been before. Looking up at them from below, Carol thought that they looked like sentinels guarding a particular piece of ocean territory. Back and forth they swam, inscribing a total composite arc of maybe two hundred yards. Whatever it had been that had caused one of the whales to vary its swimming pattern and run into Nick was certainly unclear. But Carol did not want to risk another encounter. She motioned for Nick to follow her and they swam about thirty yards away, to a sandy trench between the reefs.
Carol planned to return to the surface as soon as it was clear that Nick was not seriously hurt. But while Carol was thoroughly surveying his body to make certain that she had not overlooked any serious lacerations in her hurried check, Nick discovered two parallel indentations in the sand below him. He grabbed Carol's arm to show her what he had found. The indentations were grooved like tank tracks and were about three inches deep. They appeared to be fresh. In one direction the tracks ran toward the reef fissure underneath the three whales. In the other direction the parallel lines extended as far as Nick and Carol could see, running along the sandy trench between the two major reefs in the area.
Nick pointed up the trench and then swam away in that direction, following the tracks with fascination. He did not turn around to see if Carol were following. Carol quickly backtracked as close to the fissure as she dared (was she imagining again or were the three whales watching her as she crept along the ocean floor?) to take some pictures and to verify that the tracks did indeed emanate from the opening in the reef. She thought she saw a network of similar indentations converging just in front of the fissure, but she did not tarry long. She didn't want to be separated from Nick in this spooky place. When she turned around, he was just barely in sight. But he had fortunately stopped when he realized that Carol was not behind him. Nick made an apologetic gesture when she finally caught up with him.
At one point the parallel lines disappeared as the sandy trench turned to rock, but Nick and Carol located the continuation of the same tracks some fifty yards farther along. The trench eventually became so narrow that they were forced to swim six feet or so above it to keep from banging against the rocks and coral on either side. Soon thereafter the tracks and the trench made a left turn and disappeared under an overhang. Carol and Nick stopped and floated in the water facing each other. They carried on a conversation with hand gestures. At length, they decided that Carol would go down first to see if anything was under the overhang, since she wanted a close-up photograph of the disappearance of the tracks anyway.
Carol swam carefully down to the floor of the trench, skillfully avoiding contact with the edges of the reef on both sides. Where it disappeared under the overhang, the trench was just wide enough for her to put one of her flippered feet down lengthwise. The overhang was about eighteen inches above the floor, but there was no way she could bend down and look underneath without scraping her face or hands against the reef. Carol gingerly