CLYDE SEA AHEA. 115 



beino- -?- hours ebb at the former, and 4l hours ebb at the latter. A strong east 

 wind was blowing, leading to well marked banking up of warm surface-water against the 

 eastern side (see p. 106). The cross-section shows that the rise of surface isotherms in the 

 longitudinal section at Clynder is due to the colder water drawn up on the windward side 

 and driven across the loch. The same thing probably happened, though perhaps in a 

 less degree, elsewhere. The mass of relatively cold water which stretched along the 

 bottom from the lip of the barrier diagonally to beyond Shandon is exaggerated in 

 the section by the dividing isotherm happening to be one at which the colour is changed, 

 the temperature below 46° (or even 40° \5) being practically uniform to the bottom. 



Section XVIII., August 20th, 1888. — There were only two sets of soundings, but 

 these showed for the head of the loch the greatest range of vertical temperature ever 

 observed in summer. Below 54° at 5 fathoms the isotherms were practically parallel 

 and horizontal. Above that level they dipped landward, the water on the surface rapidly 

 growing warmer to Garelochhead. The weather was calm, and the tide rather more than 

 half ebb. 



Section XIX., September Gth, 1888. — The average mass-temperature was 54°"1, and 

 that of the upper 5 fathoms 54°*7. The isotherms showed a very slight dip landward at 

 the head, and a very slight dip seaward at the mouth, except between Row I. and II. The 

 section seems to show the commencement of seasonal cooling. A strong, squally S.W. to 

 W.S.W. wind was blowing, and the tide was about quarter ebb. 



The three Sections for June are representative of the conditions of rapid heating. 



In June J 886 there was the most perfect instance of parallel isotherms dipping 

 seaward, each of the three isotherms of which more than two points were fixed being 

 almost straight lines. The strata of water seemed in fact to be uniformly displaced or 

 tilted so as to bring up the cold lower layers against the head-slope, and to bring down 

 the warm upper layers on the barrier. 



In June 1887, with higher temperature and greater range, the isotherms were also 

 remarkably straight and parallel, dipping seaward, but more gently than in 1886. The 

 upper isotherms were somewhat irregular. 



In June 1888 the isotherms present on the whole the best example of landward dip, 

 the only other instance at all well marked of an accumulation of surface water at the 

 head being in Sections XII. and XIV., August and November 1887 — both cases of 

 flood-tide. 



All the June observations were made during the first half of ebb ; and the great range 

 of temperature makes them particularly useful for the purpose of detecting evidence 

 of the circulation of water by means of the direction of isotherms. 



The phenomena associated with the Bar off Row Point are well brought out in 

 several of the sections. Out of the whole number of 19, there are 13 sections in which 

 observations were made at Row I. and at Row II., on both sides of the shallow bar 

 which separates the Gareloch from the Estuary. In six of the cases the isotherms (with 



