
Parr IL. Sect. i. §2.] INFLUENCE OF AIR ON WATER. 327 
the surface of the globe. Upwards of 300 species of diatoms have 
been found in the deposits left by dust-showers. Among the 
millions of organisms thus transported it is hardly conceivable that 
some should not fall into a fitting locality for their continued 
existence and the perpetuation of their species. Animal forms of 
life are likewise diffused through the agency of winds. Insects 
and birds are often met with at sea many miles distant from the land 
from which they have been blown. Such organisms are in this way 
introduced into oceanic islands, as is well shown in the case of 
Bermuda. Hurricanes, by which large quantities of water are sucked 
up from lakes and rivers over which they pass, may also transport 
part of the fauna of these waters to other localities. 
: Kfflorescence products.—Among the formations due in 
large measure to atmospheric action must. be included the saline 
efflorescences which form upon the ground in the dry interior basins 
of continents. The steppes of Southern Russia, and the plains round 
the Great Salt Lake of Utah, may be taken as illustrative examples. 
Water rising by capillary attraction through the soil to the surface 
is there evaporated, leaving behind a white crust, by which the upper 
portion of the soil is covered and permeated. The incrustations 
consist of sodium chloride, sodium and calcium carbonates, calcium, 
sodium, and potassium sulphates in various proportions, these being 
the salts present also in the salt lakes of the same regions (p. 398). * 
§ 2. Influence of the Air on Water. 
The results of the action of the air upon water will be more fitly 
noticed in the section devoted to Water. It will be enough to notice 
here— 
1. Ocean currents.—-These are mainly dependent for their 
existence and direction on the circulation of the atmosphere. The 
in-streaming of air from cooler latitudes towards the equator causes 
_a drift of the sea-water in the same direction. As, owing to the 
rotation of the earth, these aerial currents tend to take a more 
and more westerly trend in approaching the equator, they com- 
municate this trend to the marine currents, which, likewise moving 
‘into regions with a greater velocity of rotation than their own, are 
all the more impelled in the same westerly direction. Hence the 
dominant equatorial current, which flows westward across the great 
ocean. Owing, however, to the position of the continents across its 
path, this great current cannot move uninterruptedly round the earth. 
It is split into branches which turn to right and left, and, bathing the 
shores of the land, carry some of the warmth of the tropics into more 
temperate latitudes. Return currents are thus generated from cooler 
latitudes towards the equator. (Section ii. § 6.) 
2. Waves.—The impulse of the wind upon a surface of water 
throws that surface into pulsations which range in size from mere 
? On efflorescence of Great Salt Lake region, see Exploration of 40th Parallel, i. sect. v. 
Consult also E. Tietze, ‘“‘ Entstehung der Salzsteppen,” Jahrb. Geol, Reichsanst. 1877. 
