What do the thirteen rows of stone mean on the US dollar bill?

They have multiple connections. The number 13 of course represents the 13 colonies that made up the original United States, the stone indicates they form the foundation of the country, the fact that the pyramid is unfinished indicates that the US is and always will be a work in progress, and finally the use of masonry relates to the fact that many of the Founding Fathers were members of the society of Masons.