Source of the Crack
Long Tian stopped in front of the crack, focusing the light from his Dragon Shadow on its surface to clearly illuminate its direction and width. The crack started from the corner on the outside of the base and extended diagonally along the texture of the stone surface for about an arm's length. At its narrowest point, it was only a line, and at its widest point, it was about a finger's width. The stone at the edge showed a fresh cross-section, without the rounded edges formed by long-term water erosion, as if it had only recently cracked.
He swam along the direction of the crack for a while, stopping near its end, and placed his palms on the stone surfaces on both sides of the crack for a moment. The aura of the Origin Return Pearl spread along the edge of the crack, and near the end of the crack, he encountered an anomaly—there was a layer of lower density inside the stone, as if there was an undiscovered dark line inside the stone that had cracked along the dark line after being subjected to long-term stress.
He withdrew his hand and hovered above the end of the crack for a while. This crack was different from all the others he had seen on the keel and underwater paving. It started from inside the structure, and there were no signs of external impact on the surface. It seemed to have been caused by the weight of the structure itself or long-term stress accumulation. He used his breath to probe the end of the crack twice more to confirm that the direction of the internal dark lines was consistent with the direction of the crack on the outer layer of the stone surface before floating back to the surface. After climbing back onto the boat, he explained his observations.
After listening to the conversation, the man at the stern squatted down by the gunwale and glanced at the underwater area without speaking immediately. He secured the gunwale, dipped his hand into the water to test the temperature, and when he withdrew his hand, his fingertips were covered with a layer of fine powder, a darker shade of grayish-brown than the grayish-white powder he had seen before. He wiped his fingers on the gunwale and said, "If it were just this one crack, so much debris wouldn't be floating on the surface. There might be a larger crack elsewhere, or this crack might lead to an internal cavity that is still peeling away."
Long Tian nodded, took out the silk map from his pouch, unfolded it on the deck, and used his fingernail to draw a thin line along the edge of the marked area at the keel base, indicating the direction and approximate length of the crack. After finishing, he put the map away, stood up, walked to the bow, and glanced at the direction in which the floating debris was scattered on the sea surface. The debris spread out from the outer edge of the shallow water area towards the northeast, continuing to drift under the current. He mentally mapped the location of the debris to the underwater structure, initially determining that the breakage should be in the outer area of the underwater paving surface, not in the core area he had previously entered.
He took off his coat, re-fastened his leather bag, and flipped himself into the water. This time, instead of swimming towards the keel, he dived down in the opposite direction of the scattered floating debris, swimming towards the northern edge of the paved area. Visibility was still poor, but the Dragon Shadow's shadow maintained a stable illumination range in the murky water. After swimming a distance along the edge of the paved area, he saw a second crack near the outer edge. This crack was much wider than the one on the keel base, wide enough to fit a hand. Debris was clearly peeling off the edges, and the surrounding stone surface was covered with a layer of freshly flaked stone dust, slowly drifting in the current. Several small horizontal cracks appeared between the paving slabs around the crack, as if they had been split open from below. The cracks extended from the main crack to both sides, intersecting with the original drainage channels on the paved surface.
He swam along the crack, confirming it was longer, wider, and more severely eroded than the previous one. He probed the stone surface at the crack's edge with the aura of the Origin Return Pearl, receiving feedback similar to the first crack—dark patterns inside, with the crack spreading along them. However, this crack had a fork at its end, leading to a deeper area beneath the paved surface. He placed his palm near the fork and felt for a moment, sensing a rhythmic vibration emanating from within, as if something below was gently striking the underside of the paved surface at a fixed frequency.
When he surfaced, it was already past sunset. After climbing back onto the boat, he squatted down by the gunwale, wiping the water from his face, and described what he had seen underwater and the continuous vibrations coming up from beneath the paved surface. After listening, the man at the stern re-secured the rudder, walked to the gunwale, squatted down, and asked, "Was that vibration a pulse of water or a collision of solids?"
"It's not like flowing water. Its rhythm is too even, like the vibrations produced by some kind of mechanical structure in continuous operation, transmitted through the pavement."