12 



REPORT — 1870. 



An attempt has been made, from the accompanying register, to estimate 

 the total quantity of sediment carried down in suspension during the year. 

 Each pair of succeeding entries in the fifth column, viz. "discharge per 

 minute," have been added together, the sum divided by 2, and the quotient 

 multiplied by the number of minutes between the observations. The result 

 is a total of 3564 tons for the year. 



The surface of the valley of the Onuy is 84 square miles ; and the effect of 

 the above result would be (taking the average specific gravity of the Silurian 

 rocks as 2-5) to reduce the level of the whole by -0025, or ^-i-jj of an inch. 

 Probably, however, the rate of denudation during the year has been exception- 

 ally low ; and, besides, no account is here taken of any but suspended matter. 



