Divers and scientists discover a rock wall 25 to 30 meters underwater near the Penghu Islands off Taiwan's western coast during an expedition earlier this year. (Courtesy of Undersea Archeological Society of R.O.C.)

The waters surrounding the offshore Penghu islands in the Taiwan Strait may contain ancient ruins belonging to a lost civilization, according to results of a preliminary study conducted by an organization formed by scientists and professional divers presented yesterday.

They may also find, however, that these underwater structures are just natural geological formations from volcanic eruptions of basalt lavas - the predominant rock type for the islands around Penghu - as some geoscientists have suggested.

Saying that they have evidence showing "possible man-made" structures in the Tong-Ji and Hsi-Ji islets, the preparation committee for the "Underwater Archaeological Society of the R.O.C." showed photographs and sonar sounding charts from their submarine investigation this past year during a press conference yesterday.

"What we found from our diving expeditions this summer is most unusual. In water depth of between 25 to 30 meters, there were flat rock walls stretching for more than 100 meters, about one meter in height and 50 centimeters in thickness. The walls were positioned in an east-west direction. Through sonar scan detection, we discovered four to five more similar rock walls in the area's vicinity," according to Steven Hsieh, leader of the group.

Hsieh claimed that some of the wall sections contained rounded cobblestones and he concluded that the long linear formation of the underwater rock structure made them most likely man-made works.

"If so, these are the legendary lost civilizations of the Penghu waters, which we have heard about in old Taiwanese folklores and myths. They would be more than 7,000 years old, and might be as much as 12,000 years old. There might have been a city there once that is now submerged under the sea," Hsieh said.

"We are forming this organization to conduct a proper scientific investigation of the area, and will hopefully get the cooperation of government agencies," said Hsieh.

However, scientists cautioned that dreams of ancient civilizations having existed in Penghu's waters are just speculation at this point, as there are natural explanations for the linear rock formations.

Professor Tsao Nu-chung, section chief at Taiwan's Central Geological Survey, said that flood basalts and other types of volcanic lava eruptions can also create the linear formations, due to inherent joints and planar structures of the igneous rocks.

"The Penghu islands came into existence from volcanic eruptions about 10 million years ago. The lava erupting from the volcano intruded into overlying rock beds could become a flat natural structure. We have seen these types of volcanic rock formation that looked like human creations. Therefore, we have to be careful before coming to conclusions," said Tsao, a geologist who has mapped volcanic rocks in the Penghu islands.

The underwater diving expeditions conducted by the group this past year were filmed and will be shown on Public Television Service network on November 25 and 26 at 9 p.m., and also presented in a documentary at 10 p.m. as part of the news magazine program.