732 REPORT — 1886. 



there are considerable differences between bottom and surface conditions 

 and between those found at high and at low tide. 

 3. The firth, where the rate of increase of salinity and of change of tempera- 

 ture, as the sea is approached, is small and proirressively diminishing ; 

 and where there is little dift'erence between bottom and surface con- 

 ditions and between the state of matters at high and at low tide. 



Some riyers have no firth, others have neither firth nor estuary ; the size, posi- 

 tion, and character of each region depending on the ratio between the volume and 

 velocity of fresh water in the river to the size and configuration of the sea-inlet 

 into which it falls, and also to some extent on the weather and on tides. 



The only British river-system which has been pretty fully investigated physi- 

 cally is that of the Forth. ^ The Clyde,- Tay,' and Spey * have been examined in a 

 preliminary manner, and the Thames^ estuary to a slight extent. Attention may 

 be specially drawn to the Thames, the Bristol Channel, the Wash, and the mouths 

 of the Mersey, Kibble, Humber, and Shannon as worthy of special study in this 

 respect. 



The observations required in such researches as carried on by the Scottish 

 Marine Station are the following, repeated monthly at intervals of a few miles 

 along the river channel from fresh water to the sea : — 



1. Temperature at surface, bottom, and intermediate depths. 



2. Density of the water as a measure of salinity at the same places. 



3. Amount of susj>ended matter and transparency. 



4. Alkalinity as a measure of dissolved' calcium carbonate. 



Messrs. Negretti and Zambia's patent standard deep-sea thermometer, in the 

 Scottish frame, and the Scottish slip water-bottle made by Mr. Frazer, Lothian 

 Street, Edinburgh, are the most convenient and trustworthy instruments for ascer- 

 taining temperature beneath the surface, and for collecting samples of water in river 

 entrances where depth is small and currents are rapid. 



(The paper was illustrated by charts, diagrams, and by the exhibition of ap- 

 paratus.) 



5. Configuration of the Clyde Water System.^ 

 By Hugh Robert Mill, D.Sc, F.B.S.E., F.C.S. 



The Clyde runs westward for 25 miles from Glasgow, gradually widens to 

 2 miles at Cloch Point, where it turns abruptly southwards and pursues this course 

 for 49 miles, rapidly attaining a width of 30 miles, which continues until it merges in 

 the Irish Channel. The southern and eastern shores are unindented, but the northern 

 is cut up by inlets averaging about three-quarters of a mile wide, and from 2^ to 

 '16 miles long. Bute, Arran, and the Cumbraes give rise to narrow cliannels in the 

 Firth ; the largest, Kilbrennan Sound, runs up into Loch Fyne, the widest of the 

 sea-lochs, and 40 miles long. This topographical description gives little idea of the 

 natural divisions of the district or of the true relations in it of laud and water. 



The large bathymetrical chart exhibited, which was made for the atithor by 

 Mr. Bartholomew, Edinburgh, is contoured and coloured to show the depths of water 

 and the heights of land. It plainly indicates the following features. A broad 

 plateau crosses the firth's mouth from the extremity of Cantyre, past the south end 



• Mill, 'Salinity of Firth of Forth,' and 'Temperature' of ditto, Proc. B.S.E. 

 xiii. (1885) 29, 157. 



^ Macadam, Brit. Assoc. Heps. 1855, Part II. p. 61 ; Mill and Morrison, communi- 

 cated to Sections A and D, this meeting. 



3 Mill, ' Salinity of Tay and of St. Andrew's Bay,' Proc. P.S.E. xiii. (1885) 347. 



■• Mill and Kitnhie, 'Rivers directly entering a Tidal Sea,' Proc. R.S.E. xiii. (1886) 

 460. 



* R. W. P. Birch, 'Passage of Upland Water through the Estuary of the Thames,' 

 Min. Proc. Inst. C.E. Ixsviii. 212; Ixxxi. 295. 



'■ Published in the Scottish Geographical Magazine, Jan. 1887. 



