The magnitude of the reservoir of water gathered at high water in the upper estuary may be gauged by the fact that spring tides rise 30 feet and neap tides 20 feet, and form the mighty power for scouring the sea channels. The riddle of how to treat the upper estuary has therefore been solved by leaving nature severely alone and permitting no interference. THE RIDDLE OF THE OUTER ESTUARY When we come to consider the conditions affecting the outward estuary, which extends from the Rock Light to the Bar, we have to take into account not only the scouring power of the ebb tide, and its capacity as a sand carrier depending upon the force of the current and the volume of water, but also the action of waves which is very powerful in preventing the undue accumulation of sand upon our shores and upon the great sandbanks lying off the entrance to the port. Standing on the shore at Blundellsands at low tide and during a westerly gale, I have seen the shore from Hightown to Seaforth a moving mass of sand, spreading itself over the surface like a sheet. Placing a stick into the ground, in a few moments a heap of sand would accumulate on the windward side. These sand storms fill up all the mouths of the Alt, and pile the sand up in big banks. If there was no correcting force these sand storms would quickly fill up the shallow shores and destroy their capacity to impound the tidal water which assists the scouring power of the main stream; but at high water with a westerly gale the waves churn up these deposits of sand, and the ebb tide carries them out to sea. After a westerly gale I have seen the shores swept of loose sand down to the hard shore beneath, and the many outlets of the Alt washed clean, and the black marl which forms their banks exposed. I do not think that this wave action has been sufficiently considered in selecting the shallow flats on the west side of the Burbo Bank as the place of deposit for the sand dredged from the Bar. They are frequently violently disturbed by the action of the waves, and the sand is carried by the flood tide back again to the Bar. There is another action of which we must take notice; every stream creates an eddy of slack water, or, it may be, a counter current of much reduced velocity, in a stream heavily charged with sand such as our tidal streams, and these eddies may create inconvenient deposits of sand and accretions to the banks which have to be watched. THE OLD SEA APPROACHES