24 Charles Darwin. 



but must have originated thousands of miles away. 

 The dust was made up to a certain extent of infus- 

 oria — minute fossil forms that could be readily trans- 

 ported by the wind, and Darwin, by the identification 

 of the fossils, was enabled to demonstrate that they 

 had been borne not from the adjacent coast of Africa, 

 but from South America, several thousand miles 

 distant. The shower referred to here was estimated 

 by the young naturalist to have a breadth of sixteen 

 hundred miles and an area equal to one million 

 square miles. 



These dust-showers produce what are known as 

 blood-rains in Europe, and Professor Ehrenberg esti- 

 mated that in one shower over seven hundred and 

 twenty thousand pounds of matter fell, out of which 

 ninety thousand pounds consisted of the remains of 

 minute animal forms. 



The dust-shower had a greater significance to our 

 young naturalist than a mere phenomenon, and 

 here we see how his every discovery or observation 

 resulted in a deduction of value to the scientific 

 world. If dust, and such large particles, could be car- 

 ried vast distances, why not seeds ? and he assumed 

 at once that the light and delicate sporules of 

 cryptogamic plants could be transported from con- 

 tinent to continent, — a thought which in later years 

 he elaborated with interesting and valuable results. 



Darwin made his first foreign geological examina- 

 tions at Porto Praya, and his report on the ancient 

 volcanic activity of the island shows how close a 

 student he was. Here he first observed tropical 

 marine forms, and the large brown sea-slug, or Aply- 



