78 DB, HUGH ROBERT MILL ON THE 



the contorted form. This is brought about in many cases by a very steep gradient at 

 the bottom of the curves, such as is rarely shown elsewhere. Curve 10, for example, 

 shows a fall of 1°*4 in the last 3 fathoms, where the gradient is almost as steep as in 

 the surface layers, and far steeper than at any intermediate point. Curve 11 also shows 

 a marked steepening of the gradient, a concave parabola below 20 fathoms. 



In No. 12, the steepest gradient in the whole curve lies between 28 and 30 fathoms ; 

 but Curve 13 (fig. 28), shows this peculiarity most strikingly. In this curve (23rd 

 September 1887) there is from the surface to 5 fathoms a fall of 1°'6, from 5 to 32 

 fathoms a net fall of 1°"1, while from 32 to 34 fathoms the fall is as great as 3° "8 in only 

 2 fathoms. This peculiarity, only noticeable between June and September 1887, and 

 comparison of the sections of the loch, shows a narrowing of the zone of rapid change of 

 temperature towards the S.W. end of the basin, the layer of rapid change of temperature 

 being usually much less clearly marked. The upper layers of water are seen by the 

 section to be more fully mixed or less affected by land at the Furnace end of the Basin 

 at all times of the year. 



There was only one case of short-interval observations, Nos. 15 and 16, on January 

 3rd and 6th, 1888. The mean temperature fell from 47°'3 to 47°'l, or at the rate of 

 0°*7 per day. The fall was 0°'4 in the top 5 fathoms, 0°'3 in the bottom 5 fathoms, 

 and, except for an irregular rise between 5 fathoms and J 5 fathoms, was fairly uniform 

 for the rest (fig. 28, Plate XXVIII. ). 



The observations at this station are most valuable, as showing the effect of the 

 sudden steepness of descent of the loch's bed on the physical condition of the 

 water. 



Observations off Strachur and Inveraray. — It is convenient to consider the two 

 deepest stations at which observations were made in the Upper Basin of Loch Fyne 

 together. The station about midway between Strachur and Kenmore was in the centre 

 of the Basin, and practically at its deepest part, although patches of equal depth occur 

 between it and Furnace. The depth is 75 fathoms, being 15 fathoms deeper than the 

 observing point between Inveraray and St Catherines. The latter may be looked on 

 as in the deepest water of the Basin also, as the slope along the axis is very uniform. 

 While the deepest water off Strachur lies nearly in the middle of the loch, that off 

 Inveraray is very much nearer the south-eastern than the north-western shore. This is 

 partly because of the widening of the loch by the large bay known as Loch Shira, and 

 partly because of the shallowing of the north-western margin by the deposits brought 

 down by the rivers Aray and Shira. 



The following summaries of the conditions at the two points show that the water at 

 Inveraray is of slightly lower salinity throughout than at Strachur. The difference at the 

 bottom is very slight, that at the surface considerably greater on account of the inflowing- 

 rivers. 



At the Strachur station the position of observation was Fairy Hill S.W. by S. ^ S. 



