TEANSACTIONS OF SECTION C. 653 



quantity diminishes to '262 grains up tlie river Trent and 202 grains near the 

 Albert Dock at Hull, while off Spurn, at the entrance to the river, there is no mud 

 in suspension, hut only a few grains of clean sand. The floor of the North Sea at 

 the entrance is covered with clean sand and shells, the beach up to Grimsby also 

 being covered with sand. 



The solid matter in suspension is derived from the detritus washed off' the land 

 and poured into the river when freshets occur, or from the erosion of the banks 

 of the river and its tributaries. The greater quantity that prevails in the more 

 turbid zone is due to the material being kept in a state of oscillation by the ebb 

 and flow of the tides when the quantity of fresh water flowing down is not suf- 

 ficient to carry it out to sea. 



The average quantity of solid matter contained in thirteen other English rivers 

 when in flood is 200 grains in a cubic foot. The average rainfall within the 

 watershed of the Humber is 29-60 inches, of which 10 inches may be taken as the 

 quantity due to such rains as produce freshets. With these figures the normal 

 total quantity of solid matter placed in suspension in floods may be put at three 

 million tons in a year. A portion of this is carried out to sea in heavy freshets 

 and the rest remains in the river in a state of oscillation. 



The tendency in all rivers, whether fresh or tidal, is for material to work down- 

 ward under the laws of gravity. The same quantity of tidal water that flows into 

 the river has to flow out again, but its capacity for transporting material down- 

 wards is reinforced by the discharge of the fresh water. 



The flood current in the Humber runs at the rate of four miles an hour, and 

 its duration varies from six hours at Spurn to two and a half at Goole. It may 

 be taken, therefore, that a particle of solid matter entering the Humber at Spurn 

 Point would not be carried by the flood tide more than 20 miles up the river, or 

 25 miles below the point where the greatest amount of solid matter is held in 

 suspension. On the turn of the tide it would be carried back again. 



Allowing for the greater time the ebb current is running above the junction of 

 the rivers, as compared with the flood, the material carried down on the ebb is 

 73 per cent, greater than that carried up on the flood. 



Taking the length of the Holderness Cliflfs as 34 miles, the average height at 

 12 yards, and the mean annual loss at 2^ yards, the mean quantity falling on the 

 beach is about If million cubic yards a year, of which about 40 per cent, consists 

 of stones, gravel, and coarse sand, leaving less than a million cubic yards to be 

 washed away. The foot of the cliff's is only reached for about four hours at high 

 water of springs, that is, by 260 tides in a year, the average quantity of alluvial 

 matter for each tide being 3,728 cubic yards. 



The drift of the tidal current towards the Humber lasts 3i hours, and runs at a 

 velocity of 2i miles an hour ; the greatest distance a particle of solid matter put iu 

 suspension at the point of mean distance, 20 miles from the Humber, could be 

 carried southward is 8f miles; when this distance is reached the tide would turn 

 and the particle would be carried northward for 16 miles, or 28 miles away from 

 the Humber. 



It is, however.quite improbable that a particle of matter placed in suspension 

 at the foot of the clifls could ever reach the main current going to the Humber. 

 Owing to the Yorkshire coast being in an embayment the main tidal current does 

 not approach nearer the coast than the 6.fathom line, or a mile away from the 

 coast. _ The current of the flowing tide sets into the embayment towards the coast. 

 Even if a particle from the clifls could overcome this shoreward set and traverse 

 the water contained in this mile of water in an opposite direction, so as to be 

 brought into the main southerly-going current, the quantity of solid matter 

 brought into suspension woidd only be sufiicient to supply one grain to 14,000 cubic 

 feet of water. 



It is evident from the above facts that it is not possible for the detritus from 

 the Yorkshire coast to reach, much more to be carried up, the Humber. 



