THE CLYDE SEA-AREA. 



391 



TABLE III. AVERAGE PERCENTAGE OF PURE SEA-WATER. 



The remarkable feature shown by this table is, that if the Gareloch be 

 excepted, the amount of pure sea-water present in the bottom water at any 

 point scarcely varies more than 2 per cent, from the average of the whole. 



There are not sufficient observations to justify us in fixing the possible 

 variations in salinity at any one point ; but it seems probable that they are 

 rarely more than correspond to an addition to the average of 5 per cent, more 

 sea-water or of 10 per cent, more fresh water. An exception may occur at 

 the head of lochs where the effect of wind in mixing the water is most felt. 



The rainfall of the Clyde Sea-area is that typical of the west coast, heavy 

 on the high ground, less so on the low ground, and everywhere showing a 

 maximum in winter (December and January being the wettest months) and 

 a minimum in early summer, the driest months being May and June. While 

 it is impossible from the small number of rainfall stations to speak with any 

 degree of certainty, it is probable that the average annual rainfall for the 

 20 years, 1866-1885, was about 56 inches on the landward portion of the 

 Clyde Sea-area and about 43 inches on the seaward portion. During 

 the investigation of salinity a clear relation w r as found between the degree 

 of dilution of the water and the amount of rain in the preceding two months. 

 There are fairly distinct indications that the normal salinity of the whole 

 mass of the water is subject to an annual variation similar but inverse to the 

 annual variation of rainfall. The rainfall minimum in May is followed by a 

 maximum -of salinity in July and August, and the rainfall maximum from 

 October to January by a salinity minimum from December to March. The 

 w^ater as a whole seems to be freshest in February and saltest in July and 

 August. 



During a severe frost the surface of the narrow sea-lochs is frequently 

 frozen over ; but in the cases I have seen this is the result of the cooling 

 during a cold eight of the ice-cold surface film of fresh water poured in from 

 the mountain slopes after a temporary thaw, and in no case was the ice 

 formed from sea-water. 



Chemistry of the Water. The chemistry of the water of the Clyde Sea- 

 area has only been partially studied. I am not acquainted with any 

 determinations of the dissolved gases in the water, and the only chemical 

 analyses of high precision to which I can refer are those carried out by Mr. 

 A. Dickie in the late Professor Dittmar's laboratory in Glasgow in 1887, and 

 those by Mr. H. N. Dickson in the Oxford University laboratory in 1896, 

 the samples in both cases having been collected mainly by myself. Mr. 

 Dickie determined Chlorine, Sulphuric Acid, and Alkalinity in 117 samples 

 collected on six trips at intervals of about two months ; Mr. Dickson 

 determined Chlorine, Sulphuric Acid, and Density by direct pyknometer 



