Sentence:  Old attitudes are held more tenaciously in the Tidewater than the Piedmont ; so that a line <WSD>running</WSD> down the length of the South marking the upper limits of tidewater would roughly divide the Old South from the new , but with , of course , important minority enclaves . 
Meaning of the word marked with <WSD> tags:  stretch out over a distance, space, time, or scope; run or extend between two points or beyond a certain point