Have you see how small the telephone directory is these days? Its more like a pamphlet than a directory! In the olden days the telephone directory was a weighty tone, so thick that it was used as one of the tasks in televised strongman competitions, to tear directories in half! Even i could tear a current one though i'd struggle with the Birmingham directory from 1980 (as below).
The directory is mostly just lists of numbers, in alphabetical order of the phone line owner. It was interesting to look through at numbers i remember from decades ago (yet i still struggle to remember my own mobile number!) In the centre of the directory is the rather fabulous Green Pages detailing the various services of the General Post Office telephone service - Post Office Telecommunications (soon to become British Telecom) which we will look at in further detail at a later time.