Geological Society of London, 93 



Plata that the depth at any point over an area of 6000 square miles 

 was not more than 30 feet, nor less than 8 feet, so that there was not 

 in that particular instance of an estuarj'' much deviation from a plane. 



Mr. Tylor does not think the plane of denudation is a good term. 

 In the Irish Sea, of which he produced a section and plan, the width 

 of the central gorge below 50 fathoms varies with the width of the 

 channel from shore to shore. The curve of denudation is a more 

 exact phrase for the section of the sea than the plane. 



Mr. Tjdor exhibited drawings and observations to prove that the 

 velocity of the tide over a district of 120,000 square miles of sea 

 bottom near Scilly is about 1 mile an hour, the mean depth of the 

 channel averaging 67 fathoms. 



By the composition of forces the velocity of the tide at springs is 

 increased in an eastward course to six knots an hour near the 

 Channel Islands, or south of the English Channel, where the Channel 

 is only 12 fathoms deep on the average. 



The tide in the more northern part of the English Channel was 

 shown from observation to increase in a regular ratio from one to 

 three knots an hour going eastward, as the depth of the sea decreased 

 from 60 fathoms to 20 fathoms. That is, as the water decreased in 

 depth, it increased in velocity. 



Mr. Tylor supported the view that the central mass of the Atlantic 

 water was moved bodily at -'oth of a mile per hour, alternately east 

 and west every six hours, and that by this rhythmic movement an 

 impulse was communicated to the water in the Irish Sea, almost 

 instantaneously, as if through a solid body. He believed he had 

 proved this transmission because the tide turned every six hours at 

 the same time in all parts of the Irish Channel, even in remote 

 Morecambe Bay. There must have been a vibration propagated with 

 the velocity almost of light from the centre to the sides of the Atlantic. 



The height of high water and the time of high and low water must 

 be affected by local influences only, for high and low water did not 

 coincide with the turn of the tide. There does not seem any evidence 

 of a tidal wave really bringing high water with it (except in a 

 funnel-shaped estuary). If it were so, high water ought always to 

 be synchronous at both ends of the Irish Channel; but the fact is 

 that it is high water at one end of the Irish Channel when it is low 

 water at the other. High and low water are only consequences of 

 the act of partly filling and emptying an irregular channel by tidal 

 impulses, and vary in time and height. 



The author does not believe in the Tidal Wave as generally 

 described by existing writers, or as a thin sheet of surface-water 

 moving at an immense velocity, according to the theory of Dr. 

 Schmick, the latest writer on the Tides. He thinks, on the con- 

 trary, all the tidal effects could be produced in a model by moving 

 the deep (tidal) impulse-giving water alternately and oppositely. 

 A central horizontal movement of _±_-inch in the deep central 

 cavity of the model would move the water at the shallow extremi- 

 ties one inch, raising and lowering the level of the water at the 

 extremities, without vertical movement of the central mass. 



