Unsolved geological problems, or what perhaps may be better described as obscure points in geological history round which conflicting hypotheses have arisen, are to be found in many parts of our Islands, but Devonshire seems to be an usually prolific field for them. Mr. W. H. Hudleston, F.R.S., in his presidential address to the Devonshire Association in 1889, enumerates nine questions propounded by Pengelly in 1868 as still requiring special consideration in the future. Of these possibly three may be said to have nearly or quite got beyond the controversial stage, but in the meantime others have arisen, and it would thus appear that the undecided position of numerous points demanding further investigation is the normal condition of a science in the developmental stage.