DIG FOR A TREASURE

Readers who met the four Guthrie children who kept things humming in Invisible Island will be delighted to meet them again when they team up with a new pair, a brother and sister lately moved to their Connecticut countryside. The two stories are not too dependent, the one on the other, but there's definite appeal in continuing familiarity -- a sort of Arthur Ransome Swallows and Amazons' feel. A treasure hunt, involving family buried treasure in a long ago Indian raid, supplies motivation for a lively story, and the island continues to play a vital part.