Complex sentence: It was officially discovered in September 1901 by pre-historians Denis Peyrony, Abbé Breuil, and Louis Capitan, but the entrance of the cave and the right-hand gallery had already been excavated by Émile River between 1891 and 1894.
Split into simpler sentences: It was officially discovered in September 1901 by pre-historians Denis Peyrony, Abbé Breuil, and Louis Capitan. The entrance of the cave and the right-hand gallery had already been excavated by Émile River between 1891 and 1894.