This paper deals with the transient deformation of surges (bores) both theoretically and experimentally. Ideal surges in open channels would normally disperse into periodic waves and be transformed to the undular bore. A train of these dispersive waves may finally reach some stable form e.g. solitary or cnoidal vwaves. In the transient process, with the development of the undulations, the height of the initial wave would not be constant as has been suggested by Keulegan-Patterson(19il-0), but would fluctuate in a complicated manner. The author indicates, theoretically, regions in which wave crests or troughs can exist and gives experimental criteria by which modes of breaking (spilling, surging or plunging) can be determined. He also believes that the curvature of the wave surface plays a leading role in the mechanism of dispersion and may act as a convective agent in the development of the undulation.