XII GEOGRAPHICAL DISTRIBUTIOX 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 o^oq-^oo-o 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 -^ wade and 

 deep. The dust from the same eruption, which fell on board 

 the ship Arabella, 970 miles from the volcano, also contained 

 solid particles y^^ inch diameter. Mr. John ^MiuTay 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 ^nnd. Taking the sp. gr. of quartz at 

 2-6, these particles would weigh about o-^.-d^o" grain each. 

 These interesting facts can, hoAvever, 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 \dolence occurred, and the region is 

 one of comparative calms. The grains of quartz found by 

 Mr. ^lurray more nearly indicate the limit, but the very 

 small portions of matter brought up by the dredge, as com- 



