CLYDE SEA AREA. 17 



surface temperature was over 50° everywhere south of Bute, but nowhere reached that 

 figure to the north of it. In the Channel, indeed, the surface temperature was somewhat 

 lower, although that at the bottom was higher, than inside the Great Plateau. 

 The general condition may be expressed by saying that the water was growing rapidly 

 warmer from the surface downward and from the ocean inward. Warming from the 

 ocean was evidently in progress, by the tide drawing inward over the great counter 

 of the Plateau slices of water from the mass, at uniform temperature of over 47°, 

 outside ; this was chilling the surface layers, but, in virtue of its superior salinity, 

 warming the lower layers. That this was the case was shown by the rapid seaward 

 slope of the isotherms in vertical sections of both branches of the Arran Basin. 

 The warming had proceeded to the greatest depth just inside the Great Plateau, 

 where 46° was found at 30 fathoms, and its influence gradually diminished landward, 

 until at Otter the isotherm of 40° reached the surface, and at Gantock rose to 

 6 fathoms. Solar surface-heating was most marked in the East Arran Basin. The 

 influence of configuration was very beautifully brought out in the deep basins of 

 Loch Goil and Loch Fyne. The bottom at Stuckbeg had the temperature 41°*9, 

 a rise of only half a degree since April, while in Loch Fj^ne the very remarkable 

 phenomenon of a mass of cold water sandwiched between warmer layers was 

 observed. 



The mass of water at uniform temperature, which made the lower part of all the 

 curves of vertical temperature in April perpendicular lines, was no longer found. There 

 was everywhere (Upper Loch Fyne excepted) a positive slope in the curve, showing 

 continuous, though not uniform, warming from the surface downward. In this trip 

 the salinity observations showed, much better than the temperature, the effect of wind 

 in setting up vertical circulation. 



Trip IIL, August 1886. — The observations (by Mr J. T. Morrison) were made in 

 two parts, the first from August 3rd to 7th inclusive, the second from the 10th to 

 the 13th. The interval between this trip and that of June was fifty days. The 

 weather of this period showed air-temperatures rather less than a degree below the 

 average for the season ; the first and last w T eek of July were hot, but the middle 

 fortnight colder, and the early part of August nearly came up to its normal warmth. 

 The prevailing wind had been south-westerly. During the trip the weather was 

 broken, several small cyclones passing and producing variable light winds, usually from 

 the south-west, and blowing up most of the lochs. 



The distribution of temperature was practically the same as in June, although 

 the water was, throughout, warmer. In the North Channel the whole mass of oceanic 

 water, remaining homothermic, had warmed up to 52° '7, and pouring over the Great 

 Plateau, as in June, cooled the upper and warmed the lower layers in the Arran 

 Basin. The isotherms on the sections from Channel to loch-heads dipped, as before, 

 strongly seaward. As before, the water in the deeper parts of the Arran Basin had 

 warmed more slowly than that outside, and remained colder, being 46° at 50 fathoms, 



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



