904 Wlarvels of the Universe 
altogether Rocks consisting of harder and_ softer 
particles undergo curious changes, the former parts 
persisting, the latter being removed by the denuding 
agencies. The ors of Cornwall afford striking 
examples of this weathering effect, a number of blocks 
piled one upon another often having a very top-heavy 
appearance, their softer materials having been removed, 
leaving the harder granitic masses remaining. On 
shores where stretches of sand are left dry the action 
of wind in modifying the surface is well shown. Sand 
dunes, or hillocks, are thus produced by the accumula- 
tion of wind-borne particles, sometimes deposited in a 
manner resembling stratification, in roughly horizontal 
layers piled upon one another. In Western Europe 
blown sand occupies a large part of the coast from 
Photo by] [A. Leal. Spain to the Baltic, advancing at the rate of three to 
if . 
See EES: twenty-four feet per year. Sand dunes of a height of 
The variety of these flint needles which sup- r; = - 
He. hs ania ce cis) Guanes fo tietdtnn. over one hundred feet are met with on the shores of 
Sponges) are) grouped according) to their; spicules: Lake Michigan, and forests and even low hills have 
been buried by the forward movement of the wind-driven particles (Geikie’s “ Geology,” p. 443). 
The deposit of yellowish clay or loam, first noticed in the valley of the Rhine, but met with in 
many other places also, known as Joess, consisting mainly of hydrated silicate of alumina (clay), 
with grains of quartz, flakes of mica, and sometimes lime, was considered by Richthofen to be due 
to the long-continued drifting and deposit of fine dust by wind over areas more or less covered by 
grassy vegetation, but Dr. Davison has since suggested that loess is best explained on the supposition 
that it has resulted from snowdrift. 
The great ocean currents are due, in part at least, to the action of Wind. |The Winds not only 
agitate the sea and produce irregular waves, but, where they are continually blowing in one direc- 
tion, they cause the surface water of the ocean to take a similar course. Of these resulting (ocean) 
currents the best known, and to us the most bene- 
ficial, is the Gulf Stream, a body of warm water 
coming from the Gulf of Mexico. Passing north- 
wards, it runs parallel to the eastern coast of the 
United States almost as far as Newfoundland, then 
turns north-eastwards towards the Azores, where it 
divides, one portion going past these islands and to 
the north of Norway; the other part bends more to 
the right, passes the coast of Portugal, and then runs 
back in a westerly direction to the West Indies. Partly 
as a result of this warm current, but still more as a 
consequence of the influx of moisture-laden air from 
these warmer regions, which, condensing, sets free heat, 
our climate is so much milder than that corresponding 
to similar latitudes in other parts of the globe. 
The polar current of the North Atlantic, on 
the other hand, is a_ cold-carrier, whose course 
SECTION OF A SPONGE. nei 
Showing. thev-channele: form hon imeeenclireet southwards from Baffin’s Bay influences the tem- 
currents lols water jand|jthe @whipyi chambers awhere aE pera tine molt ne met anti CmCOaS tO LEAT eri Came inmEnlie 
the absorption of nutrition takes place. This 
section is of a complex Sponge. opposite sense to that in which the Gulf Stream 
