170 THE AMERICAN MONTHLY [June, 



miles from the desert source suggested by Dr. S. is excessive, as 

 it is well known that such light dust floats to much greater dis- 

 tances. At the time of the Krakatoa eruption, a remarkable 

 example, only ten years ago, its dust darkened the air for ships 

 that were not within sight of the mountain, burying their decks 

 inches deep in dirt ; it whitened the decks of vessels more than 

 i,ooo miles away, and it was noticed and identified at a distance 

 of from three to four thousand miles. And it will be remembered 

 that Ehrenberg believed, whether prudently or not, that he rec- 

 ognized organisms from Africa in the air of Berlin, and from 

 America in the air of Portugal, the former, presumably, having 

 made an aerial voyage across the Mediterranean sea and the 

 European continent, and the latter across one of the widest stretches 

 of the Atlantic ocean. 



This specimen does not seem to present the familiar character- 

 istics of volcanic dust — glassy, crystalline particles of angular 

 fracture and containing minute, and often elongated, bubbles 

 from gases that were imprisoned in the fluid mass ; nor the 

 beaded forms and drawn-out vitreous threads suggestive of arti- 

 ficial furnaces and neighboring chimneys. Nor would such 

 structures be expected to be found in connection with these 

 numerous and well-preserved organic remains. 



The well-known power of fine dust-particles to precipitate 

 atmospheric moisture around them, and form a fog or haze, is 

 doubtless illustrated in the three days' fog in which this dust was 

 collected. 



The most puzzling feature of the mount is the large quantity 

 of cotton and other fibres. Considering the amount of this and 

 the character of the collector, the most common source of such 

 admixture — contamination by carelessness while preparing the 

 mount — may be left quite out of the question. And, for the 

 same reason, it may be considered as improbable as it could be in 

 any case, that the collection itself was of a mixed character. 

 Doubtless it was as pure as could be obtained on the ship at that 

 time. Yet the writer finds it impossible to believe, on the present 

 evidence, that the fibres were a part of the original dust — a con- 

 clusion extremely improbable and incompatible with what has 

 been observed during his many years of interest in this study oi 

 atmospheric dust. It is nearly incredible that textile fibres existed 

 in any such proportion along with the vast quantity of mineral 

 dust that furnished the original supply ; and if they did, they 

 differ from the rest so completely in size, form, density and 

 physical character generally that they would be very unequally 

 affected by the buoyancy of the air and by the drifting power of 

 the ever-varying wind, and they could never have kept company 

 with the finer particles during an aerial voyage of hundreds of 

 miles. It is much easier, and in fact inevitable, to conclude that 

 they belonged to the local dust of the ship itself, which by some 

 unsuspected means, as for instance by the flapping of the sails, 

 had become mixed with the " infusorial earth " from Africa. 



