THIS is the fifth of the Holiday Talks designed to give listeners some idea of the attractions of various sorts of holidays in various places at home and abroad. Today they will hear of the rugged beauties of the Border country; the wild hills over which the Romans drove their great wall, the heathy fastnesses whence the moss-troopers rode down on their forays, where Douglas and Percy waged their age-long war. Mr. Logan Mack has written an interesting book about the Border line, which he knows so well.