Archaeologists have discovered silicified woods in northwest China, which experts say date back to about 180 million years ago.

The discovery is of great value for the scientific research on geology, geomorphology and paleobiofossil in the area, archaeologists said.

The woodstones, also called paleobio fossils, are regarded as natural relics that can not be regenerated, archaeologists said, adding that they are important tangible evidence for the study of geography, climate, earth evolution and environment.

The silicified woods cover an area the size of a football fieldin Baota district of Yanan in northwest China's Shaanxi Province.

According to archaeologists, silicified woods came from woods buried deep underground hundreds of thousands of years ago. They became fossilified after having been soaked by silicate for a verylong time.

The woodstones still bear clear grains and annual rings when unearthed,archaeologists said.

Some of the woodstones have been unearthed and placed at randomon one side of the hill where they were discovered, while the restare still buried underground.

"Those woodstones stay underground vertically and in a concentrated area, which is fairly rare in terms of the distribution of fossils," said Zhang Huaibin, who discovered the silicified woods.

"I hope government departments concerned attach importance to the protection of the rare natural relics," Zhang said.

(Xinhua News Agency July 27, 2005)