Approaching the base of the cloud.
The rills mentioned earlier may continue to develop, merge and grow into large gullies, just like hillslope gullies on any other rock type. Examples are visible here. However, on limestone, once big enough to intercept the underlying fault pattern of the bedrock, water will cut downwards, vanishing underground into cave systems, so one may note that the gullies in this image are rather short and stop abruptly. [Care to see this view without the cloud?]