XCii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [April I914, 



It proved, in the first place, far from easy to find rivers suitable 

 for the investigation. The rivers draining into the fens were found 

 to be too difficult to gauge. They have a number of outlets, and 

 the discharge is effected largely by artificial means. Accessibility 

 was an important consideration, and in the Thames, which for 

 this and other reasons was the first to come to mind, the natural 

 conditions are altered, more completely perhaps than in any other 

 river, by canalization. 



Eventually, the Exe and the Medway were selected as rivers of 

 strongly-contrasted types. The Exe drains a hill-district largely 

 composed of Palaeozoic rocks, and may be described as a clear and 

 lively mountain-stream ; the Medway drains a comparatively 

 low tract of Mesozoic rocks, and may be described as a sluggish 

 lowland river. The Exe for the most part is uncontrolled by 

 weirs ; the Medway is canalized. Subsequently the Severn, another 

 canalized river, was added to the list in consideration of its im- 

 portance among British rivers, and of the fact that an elaborate 

 series of unpublished gaugings was available for our use. 



The methods of measuring the discharge are described in our 

 reports, and need not now be mentioned further than to say that 

 they were based on a determination of the relation between the 

 level of the water and the velocity of the current. Similarly, it 

 was sought to establish a relation between the suspended and 

 dissolved impurities and the level of the water. The level was 

 therefore observed daily, and even hourly in time of flood, through- 

 out the period of investigation ; and, from these observations, the 

 annual discharge and the amount of impurity proper to any 

 discharge were estimated. 



Arrangements were, therefore, made for the determination of the 

 suspended and dissolved matter in samples of water collected in all 

 conditions of the rivers. This work, w T hich was undertaken by the 

 chemical instructors of institutions in Exeter, Chatham, and Wor- 

 cester, proved arduous, for the seizing of the proper moment for the 

 collecting of samples was found to be essential, especially in the case 

 of the Exe, a lively and sensitive river subject to rapidly changing 

 moods. Special journeys were undertaken in the hope of catching 

 a flood at its height, but were often not attended with success. 

 Notwithstanding these disappointments, and despite the difficulty 

 that the chemists could not allow the work to interfere with 

 their professional duties, enough was done by them to show that 

 here we have a subject well worthy of precise and continued 



