What or who does 'the rick-thatcher' refer to in Middlemarch by George Eliot?

thatch

to make a roof for a building with straw or reeds

-Cambridge

rick

a stack of hay, corn, straw, or similar material, especially one formerly built into a regular shape and thatched.

A rick-thatcher would thatch rick (or stack).

Until the middle of the last century, perhaps more than half of all the thatching carried out in Britain, was this type of work… Stacks and ricks dotted the countryside and filled the farmyard. Cereals of every type were stored, awaiting the thresher; hay was kept dry for a winter’s feeding; all safe under a thatched covering. This employment kept the craft alive, when domestic thatching was in serious decline…

Most British people would know what a thatcher does. We still have thatched buildings, and they have become popular again recently for ecological reasons.