This 1871 postmark is on, what could be, a penny red. Difficult to be sure, as the colour is so faded and degraded with ink and dirt. 
Penny reds seem to sell for between £5 and £500,000 (almost the price of today's stamps, I hear you say.)
Awful weather, so hopefully this will fit today's TT theme. 

Many thanks to Ilje for hosting.