CLYDE SEA AREA. 49 



represent the distribution of temperature in depth, the isotherms ran nearly straight from 

 the Arran coast across the deep water until the depth diminished to 25 fathoms on the 

 coast of Ayr ; the temperature at 15 fathoms being 53 o, 0, and at 25 lathoms 51 o, 0. But 

 at this line, about 3 miles from the shore, the isotherms suddenly dipped, 55° being the 

 bottom temperature when the depth became 15 fathoms. This indicates the accumula- 

 tion of a belt of warm water along the gently sloping shore to a distance of three miles. 

 The strip of water, from the land down to the depth of 15 fathoms, had an average 

 temperature about 56°, while the average of the surface stratum 15 fathoms thick, across 

 the Basin to the edge of the warm water, was about 54°. The weather during this trip 

 was fine, with a light south wind blowing at right angles to the plane of the section, and 

 a slightly ruffled sea. 



On September 20th, 1887, two cross-sections were made in perfectly calm weather, the 

 day being very warm, with slight haze. The first series of observations, from the 

 depression between Garroch Head and Cumbrae Light to Brodick, showed the lower 

 isotherms running horizontally. That of 52° coincided with the depth of 40 fathoms ; 

 water below this temperature was confined to the deep part of the East Arran Basin, and 

 did not cross the ridge into the depression of the north-east branch. The isotherm of 

 53° was horizontal at 30 fathoms until within 2 miles of the Garroch Head sounding, 

 when it dipped suddenly. The isotherms of 54° and 55° were curved. The former 

 was at 30 fathoms off Garroch Head, rose to 15 fathoms in the deepest part of the trough, 

 and sank to 21 fathoms against the Arran coast. The isotherm of 55° rose from 

 1 5 fathoms, 2 miles from Garroch Head, to the surface at the deepest sounding, and sank 

 to 1 8 fathoms against the Arran coast. This showed that the upper layers of the deepest 

 water were on the average, at the same plane, nearly a degree colder than the water along 

 the coast. 



A more important section was then made from Brodick Bay to Irvine, a distance of 18^ 

 miles. The section drawn from the observations is given in fig. 12, Plate XXIV. The 

 of surface temperature was practically constant at 56° all the way over, and until the depth 

 45 fathoms was reached, beyond the deepest trough, the other isotherms ran in the main 

 horizontally, 55° at about 15 fathoms, 54° at about 23, and 53° at about 30 fathoms. 

 But when the depth of 30 fathoms was reached, 2^ miles further, and 4^ miles from the 

 Ayrshire coast, the bottom temperature was over 55°, so that the isotherms must have 

 dipped very abruptly. On this occasion the upper layer of 30 fathoms had an average 

 temperature of about 54°'7 all the way from the Arran coast for 11| miles, until the 

 depth of 45 fathoms on the Ayrshire coast was reached, where it met a body of shallow 

 water 7 miles wide, averaging 55° - 6 in temperature. Here there was a smaller actual 

 difference of temperature between the deep and the shallow water than in August 1886, 

 but a very much larger quantity of water had been affected by the heating power of the 

 shallows. 



Since so few observations were taken along the wide shallow coast of Ayr, it is 

 obviously impossible from the data collected to estimate the total heat content of the 



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



