CLYDE SEA AREA. 137 



layers comparable with that of Loch Goil, though much less marked. In 1886, the 

 diagram shows that the surface water was above 50° from July 10th to October 18th, or 

 three weeks shorter than at Stuckbeg, but the temperature of 50° reached the bottom by 

 October 15th, and the water there remained warmer than 50° until December 5th, 

 whereas in Loch Goil the maximum depth to which this isotherm reached was 1 8 fathoms 

 on November 12th. In 1887, the surface was over 50° from June 12th until November 

 12th, and the bottom was at or above this temperature from November 20th until 

 December 5th, whereas in Loch Goil the greatest depth reached by the isotherm was 

 20 fathoms on November 28th. The persistent low temperature of the lower layers in 

 the summer of 1887 was remarkable. In 1888, the surface was above 50° from July 7th 

 until after the end of October, but on this occasion the greatest depth reached by the 

 isotherm was 25 fathoms on September 24th, contrasted with a depth of 11 fathoms on 

 September 3rd in Loch Goil. The isotherms became vertical at the minima, showing the 

 phenomenon of homothermic change for a considerable time before and after that 

 period. 



Temperature Sections of Loch Strivan. — These sections (figs. I. to XXIIL, Plates 

 XIX. and XX.) are twenty-three in number. 



I. lith April 1886. — A general seaward dip was noticeable in the upper isotherms, 

 corresponding to a northerly breeze blowing almost directly down the loch ; but below 

 the depth of 5 fathoms the water was practically homothermic. 



II. 17th-lSth June 1886. — The water was well stratified in temperature, all the 

 isotherms showing a pronounced seaward dip. The isotherm of 45° was 1 fathom deep at 

 the head, and 15 fathoms at Bogany, while that of 43° dipped from 4 fathoms at the 

 head to 40 fathoms half-way down the loch. The wind, on both days varied from north- 

 west, light, to N.N.W., fresh, blowing straight down the loch, and obviously driving the 

 warm surface water seaward while the deeper layers welled up at the head. This fact was 

 proved absolutely by density observations, showing that the surface water at the head of 

 the loch was as salt as the bottom water in the deepest place, while the surface water at 

 Bogany was very much fresher. On this occasion the surface water at the head of Loch 

 Strivan was Salter than that at any other observed position in the Clyde Sea Area. The 

 tide in Loch Strivan on this occasion was about half-flood, so that it tended to reduce the 

 effect of wind circulation. 



III. 7 th August 1886. — The temperature throughout had increased rapidly since June, 

 but the slope of the isotherms was still seaward in the main. In the upper part of the 

 loch the isotherms were close and horizontal, indicating rapid surface-heating, probably 

 due to the warmth of the air. The wind varied from N.N.W. to west, and was light ; 

 on the previous day it had been southerly. 



IV. 25th September 1886. — A very marked rise of temperature had taken place 

 mamly, it would appear, by the entrance of warm and nearly homothermic water from 

 the Dunoon or Arran Basin. The ill-defined barrier at Bogany now served to separate 

 water with temperatures from 50° to 48° from the warmer water at 51° to 53° outside. 



VOL. XXXVIII. PART I. (NO. 1.) S 



