A SURVEY OF THE LOWER TEES MARSHES 1 25 



At several points in its steep sides erosion has ta]<eii place, 

 and at no spot is this more marked than at X where the scooping 

 motion, induced by the changing path of the inrushing tide, 

 has bitten out a semicircular opening. Contemporaneously 

 with this, whilst yet travelling in a direct line, the water has 

 undermined both sides of the narrow neck at Y leaving the 

 interlacing vegetation intact. Inevitably, both sides will 

 collapse and by falling across meet to form an underground 

 channel such as already exists at U. This will persist for 

 some time only to be closed finally when some tide more 

 powerful than usual drifts up sufficient rubbish to block it, just 

 as has happened with that at U\ At the same time as these 

 events are happening-, silt deposited at the angle opposite the 

 rounded excavation will be consolidated by Glyceria roots; 

 therefore, when the tide is forbidden access, we have formed 

 a deep pool with an almost perpendicular bank on one side, 

 and a partly colonised silt bank on the other. Then wind 

 action plays its part, and swirling eddies, set in motion, 

 displace the barer silt and convey it to level up the floor; 

 thus a sharply cut edge appears to limit the Glyceria bed 

 which, by its growth and decay, speedily raises the level on 

 that side. By their swirl, aided by the contour of the stabler 

 deeper portion, it will be perceived that these currents will 

 tend to produce a pan of circular outline. 



Still investigating the same system, let us consider the 

 channel pans at D. These primarily appeared as local 

 broadenings of the channel through tidal action and were, 

 in consequence, when developed, continuous. When all 

 advancement along their original path was impossible they 

 overflowed, and the shallower lower set was formed as a single 

 pan. But, as we have recognised, the outlet (and inlet !) at U 

 fell in and was obstructed, and their water supply thus 

 restricted to surface water. Retrogression set in, and the 

 compound pan began to deteriorate into a series of pools. 

 Just prior to this, when as yet the channel was provided with 

 moving water, the division between the extreme member of the 

 channel series and the primary pan E had been driven in to 



