* Cirrus clouds are high-altitude clouds, typically forming above 6,000 meters (20,000 feet). They are made of ice crystals and appear as wispy, feathery strands.

* Stratus clouds are low-altitude clouds, generally forming below 2,000 meters (6,500 feet). They are often layered and appear as a gray sheet covering the sky.

So, the clouds that form above 6,000 meters are cirrus clouds.