156 Rev. J. D. La Touche — On River Sediment. 



EXPLANATIOJSr OF PLATES Y. AND VI. 

 PLATE V. 

 Flemingites Pedroanus. 



Fragment of a stem showing the permanent bases of the petioles attached, 

 and imbricating. 



Sporangium laid open showing the granulated contents. — Greatly mag- 

 nified. 



Upper surface of a sporangium. — Greatly magnified. 



Sporangium, magnified to the same scale as those of F. gracilis. — Geol. 

 Mag., Vol. II., Plate XII. 



Sporangium with part of the upper surface removed, and showing the 

 depression in the interior produced by the inferior tri-radial ridge. — 

 Greatly magnified. 



Fragment of leaf shelving the parallel venation. 



Termination of a branch showing the solid axis, permanent bases of the 

 petioles, and leaves. 



Fragment of a branch. 



A few scars from Pig. 10 magnified four times. 

 PLATE VI. 



Naggerathia obovaia (natural size). 



Portion of a pinna of Odontopteris Flantiana. 



Lower pinnule of the same (both natural size). 



Fig. 



1. 



Fzg. 



2. 



Fig. 

 Fig. 



3. 



4. 



Fig. 



5. 



Fig. 

 Fig. 



6. 



7. 



Fig. 



Fig. 

 Fig. 

 Fig. 



8. 



9. 

 10. 

 11. 



Fig. 

 Fig. 

 Pig. 



1. 

 2. 

 3. 



rV. — On the Measurement of Eivek-sediment. 

 By the Eev. J. D. La Touche. 



ALLOW me to call the attention of your readers to an investiga- 

 tion wLich promises to be of considerable geological importance, 

 and which might be pursued in many places without any difficulty 

 — I mean the determination of the quantity of sediment carried 

 down to the sea by rivers. 



Obviously, if this could be ascertained, we should have some 

 measure of the rate of denudation of the surface of the country, and 

 that vagueness which attends most calculations relating to geological 

 epochs would, in some degree, be removed. 



For this purpose it will be, perhaps, best to detail some experi- 

 ments which I have myself been making with this view, upon the 

 Eiver Onny which flows by my house. 



1st. A tolerably straight and uniform reach of the river was 

 chosen, and along the bank 100 feet were measured and marked by 

 pegs driven into the ground. Here a marked post was erected in 

 the water, to take the height of the flood from time to time. This 

 is done every day after any considerable fall of rain, and at the same 

 time the rate at which the centre of the stream moves is ascertained, 

 by counting with a watch the number of seconds any floating sub- 

 stance takes to pass the measured 100 feet. 



2nd. An accurate section of the river is made by sounding. 

 From these data the number of cubic feet of water which pass this 

 point in a given time can be calculated, by knowing the ratio of the 

 speed of the centre, to the mean velocity of the whole stream, I am 

 informed by an able practical engineer, who has had much experi- 

 ence in this matter, that this is represented by the fraction four- 



