512 Mr. L. F. Vernon-Harcourt. 



from boxwood and lignum vitse swelled in water, and was carried 

 along so very easily by the stream that no definite channels were 

 formed in it. The powder obtained from Bath brick, which was 

 experimented upon for some time in the model, both without and with 

 training walls, yielded more satisfactory results, as besides affording 

 shifting channels like the silver sand; it accumulated at the sides of 

 the estuary when the training walls were introduced in the model. It, 

 however, gradually became too compact, so that the current could no 

 longer produce much effect on it ; but as it is probable that some 

 sticky material is used in the manufacture of Bath bricks, it is quite 

 possible that if T had succeeded in my endeavour to obtain the silt of 

 .the River Parret, from, which the bricks are made, in its natural 

 state, the material might have proved more subject to scouring 

 influence. 



. A_t last, in July 1887, 1 found a fine sand, on Chobham Common, 

 belonging to the Bagshot beds, with a small admixture of peat. This 

 .sand, besides containing some very fine particles, was perfectly clean, 

 so that water readily percolated through it ; and it accordingly com- 

 bined the advantages possessed by silver sand with a considerably 

 greater fineness. 



Results of Working Model with .Bagshot Sand. The bed of the 

 .estuary having been formed with the sand obtained from Chobham 

 Common, after the model had been worked for some time, the channels 

 assumed a form very closely resembling the chart of the Seine 

 estuary of 1834.* Accordingly, the first stage of the investigation 

 ;was duly accomplished by the reproduction of a former state of the 

 ,estuary in the model, with the single exception of a decidedly smaller 

 depth in the channels, except in places where the scour was consider- 

 able, which is readily accounted for by the circumstances of the case. 

 It is probable that with a larger model, and especially if the bed was 

 ,not so nearly level as in the Seine, the depth would approach nearer 

 to the proper distorted proportion as compared with the width. 



The close correspondence of the channels in the model with an 

 .actual state of the estuary in its natural condition, confirms, in a con- 

 siderably more complicated case, the results previously achieved by 

 Professor Reynolds with reference to the upper estuary of the Mersey, 

 .and affords a fair certainty that, with adequate data, the natural con- 

 dition of any estuary could be reproduced on a small scale in a model. 



Introduction of the Existing Training Walls in the Model. The 

 second stage of the investigation consisted in the introduction of 

 training walls into the model, corresponding in position to the actual 

 training walls established in the estuary down to Berville. These 

 walls, formed with strips of tin, cut to the corresponding heights at 

 Jho different places, and bent to the proper lines, were gradually 



* ' Instit. Civ. Engin. Proc.,' vol. 84, Plate 5, fig. 1 1. 



