In this paper, we investigate the chain properties of the mar "as" construction in Modern Irish, and show that it only allows the chains headed by the COMP aL, such as (aL, t), (aL, aL, t), and (aL, aN, it). We then go on to argue that this suggests (i) that there should be an agreement relationship between the head of the chain and the element that the chain is dependent on, (ii) that given (i), there should exist an independent head above C, and (iii) that uniform A'-movement actually has four chain types in language: (aN, aN), (aL, aN), (aL, aL, t), and (aL, aN, it), which indicates that the chain structures of uniform A'-chains are not literally uniform.