Two hardback Enid Blyton books, without dust-jackets, or a date, published by Collins. I believe they are 1960s. The covers are bright yellow. One is MYSTERY STORIES, THE SECRET OF CLIFFE CASTLE and SMUGGLER BEN i.e.  a two-for-one book and the other is ADVENTURE STORIES, MISCHIEF AT ST ROLLO'S and  CHILDREN OF KIDILLIN. One book has some marks on the front cover but they are fairly clean.