LONDON: Two of Charles Darwin's notebooks containing his pioneering ideas on evolution and his famous "Tree of Life" sketch are missing, believed stolen, the Cambridge University Library said on Tuesday.

The British scientist filled the leather notebooks in 1837 after returning from his voyage on the HMS Beagle. The library said they were worth millions of pounds.

In one book, he drew a diagram showing several possibilities for the evolution of a species and later published a more developed illustration in his 1859 book "On the Origin of Species".

The University of Cambridge's vast library first listed the notebooks as missing in 2001 after they were moved out of the Special Collections Strong Rooms for photography to be carried out there. They were long believed to have been incorrectly filed within the building, which contains around 10 million books, maps and manuscripts and has one of the world's most significant Darwin archives.