 He made good use of the ship's excellent library of books on natural history, but continually questioned their correctness.Geology was Darwin's "principal pursuit" on the expedition and his notes on that subject were almost four times larger than his zoology notes, although he kept extensive records on both.During the voyage, he wrote to his sister that "there is nothing like geology; the pleasure of the first days partridge shooting or first days hunting cannot be compared to finding a fine group of fossil bones, which tell their story of former times with almost a living tongue".