ANTIQUE STONE EARLY 20th CENTURY CHILDREN'S BUILDING BLOCKS.  These maybe even earlier.  I am presuming these were my father in laws when he was a child, going by the initials on one of them.  My husband is 77 so that will give you an idea of age but they could even have been his dads.  They are not in perfect condition, some have chips, some have letters written on them, some have numbers and the little flat ones have "eggs" and "butter written on them.  Please see photos.  They weigh over 2 kg.