Dover museum is a fount of knowledge on the town and there are many links from there.
I take it you mean Dover, Kent, UK! http://www.dover.gov.uk/museum/
Most industry now is based on the services sector - associated with the port and the cross-Channel ferries. This has grown steadily over the period you quote because of the growth in freight traffic associated with trade with the countries in the EU (or beyond).
Coal mining in E Kent used to be a significant employer. It is now zero.