From the Southern Travellers Handbook for 1965/66 #8
At one time there were also 'third class' carriages which were not only windowless but roofless as well...
...The rattling pig-pens on wheels, misnamed third-class carriages (before the late alterations) were despicable affairs, with the wonderful property if always meeting the rain in whatever quarter the wind might be blowing. They were a species of horizontal shower-bath, from whose searching power there was no escape.
The series is: From the Southern Travellers Handbook for 1965/66