Considering the simplest case that can be rhythmic, a minimum of three sedimentary layers &dash. light, medium and heavy; 1, 2, 3 &dash. can be permuted into six possible relationships. 
Experience, and tradition, teach that their orderly sequence is most readily understood and welcomed when sandwich effect is avoided. 
Reading from top to bottom, the series 1, 2, 3 is known as architectural form, an unfortunate and misleading phrase <tag "515673">derived</> from the bottom weighting of masonry, necessary to its stability.   

