India's Supreme Court has asked the companies that produce Coca-Cola and Pepsi to answer allegations that they painted large areas of rock face in the Himalayan mountains with advertisements. Environmentalists are concerned about the damage the advertisements may have caused to the area's ecology.

The rocks that have been painted with advertisements jut out from the mountainside along a 56-kilometer highway that leads to the breathtaking, snow-covered Rohtang pass in the northern Himachal Pradesh state. Tens-of-thousands of tourists travel the winding, mountain road every year to see the spectacular, picture-postcard scenery, nearly 4,000 meters up in the Himalayas.

The Supreme Court issued notices to the two cola companies, after a national newspaper published photographs of the rocks and quoted experts as saying that the paint has damaged the ecology of the area. The Himalayan mountain chain is the youngest and highest in the world and, experts say, the rocks support mosses and other organisms.

Geologists are also alarmed because rocks conceal many secrets of the earth's formation. They say these may be lost forever beneath the coat of paint that now covers them.

Former Director of the Geological Survey of India, Om Narain Bhargava, says the Himalayan mountain chain is among the best places for research. "Since it is a very young mountain chain, very many evidences are preserved, and, when we study these rocks, it can form a sort of case history, which can be applied to other mountain chains, also. That is the uniqueness of the Himalayas. By the painting of these rocks, we conceal some of these features, or some of the crucial evidences," he said.

Both Pepsi and Coca-Cola say the advertisements were placed by local affiliates, without their knowledge. Both companies are promising to rectify the damage.

A spokesman for the Coca-Cola company, Nantoo Banerjee, said the company is engaging geologists to advise on restoration of the rocks.

"We very much regret that this has occurred. We have instructed our people in the region to take expeditious steps to set right any damage caused by the act, in a manner that preserves, protects and enhances the environment in the area," Mr. Banerjee said.

But experts say that may be easier said than done. They say the chemicals needed to remove the paint could cause further damage, and the micro-organisms and moss that covered the rock surface are lost forever.

The advertisements are not the only environmental threat to the region. The popular tourist spot is also polluted by tons of garbage dumped by tourists. Local authorities recently joined hands with mountain dwellers to remove truck loads of plastic bags, bottles and tin cans that were littering the mountainside.