Khao Daeng is the outstanding Ordovician reddish brown limestone mountain. Various kinds of fossils have been found in the limestone such as nautiloids, amonoids, sponges and Maclurites (gastropod). The most interesting is the stromatolites in the limestone. The stromatolites played an important role on evolution of lives since they were no free oxygen prior to Cambrian period but the srtomatolites were the oxygen supplier for living things during Cambrian period.