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GEOGRAPHICAL DISTRIBUTION OF ORGANISMS 
363 
brought, but as it had been carried to a great height, it was 
in a position to be conveyed to almost any distance by a 
violent wind, had such occurred at the time. 
Mineral Matter carried by the Wind. 
The numerous cases of sand and volcanic dust being carried 
enormous distances through the atmosphere sufficiently prove 
the importance of wind as a carrier of solid matter, but un¬ 
fortunately the matter collected has not been hitherto examined 
with a view to determine the maximum size and weight of the 
particles. A few facts, however, have been kindly furnished 
me by Professor Judd, F.R.S. Some dust which fell at 
Genoa on 15th October 1885, and was believed to have been 
brought from the African desert, consisted of quartz, horn¬ 
blende, and other minerals, and contained particles having a 
diameter of inch, each weighing grain. This 
dust had probably travelled over 600 miles. In the dust from 
Krakatoa, which fell at Batavia, about 100 miles distant, 
during the great eruption, there are many solid particles even 
larger than those mentioned above. Some of this dust was given 
me by Professor Judd, and I found in it several ovoid particles 
of a much larger size, being inch long, and T V wide and 
deep. The dust from the same eruption, which fell on board 
the ship Arabella , 970 miles from the volcano, also contained 
solid particles inch diameter. Mr. John Murray of the 
Challenger Expedition writes to me that he finds in the deep 
sea deposits 500 and even 700 miles west of the coast of 
Africa, rounded particles of quartz, having a diameter of 
inch, and similar particles are found at equally great 
distances from the south-west coasts of Australia; and he 
considers these to be atmospheric dust carried to that 
distance by the wind. Taking the sp. gr. of quartz at 
2 - 6, these particles would weigh about 2 5 ioo grain each. 
These interesting facts can, however, by no means be taken 
as indicating the extreme limits of the power of wind in 
carrying solid particles. During the Krakatoa eruption 
no gale of special violence occurred, and the region is 
one of comparative calms. The grains of quartz found by 
Mr. Murray more nearly indicate the limit, but the very 
small portions of matter brought up by the dredge, as com- 
