FOSSIL INFUSORIA. 63 



remained in the guano-bed for an unknown length of time, subjected to those 

 common causes of decay which turn the solid rock itself to dust. But under 

 all these influences they continue unchanged, and the eye of the naturalist at 

 last detects these minute structures still possessing their original beauty, with 

 the delicate tracery of their rich configurations, almost as sharp and clear as it 

 was, perhaps, a thousand years ago. 



INFUSORIAL DUST. The fossil shells of animalcules, which lie mingled with 

 the. soil of the earth, are not unfrequently carried up into the air in the clouds 

 of dust that are raised aloft by the winds, and borne along on the currents of 

 the atmosphere, to a distance almost incredible. Darwin noticed that the atmos- 

 phere of St. Jago, one of the Cape de Verde isles, is generally hazy, owing to 

 the fall of an impalpable fine dust, of a brown color. A small quantity of the dust 

 was collected by this gentleman, who received also, from Mr. Lyell, four packets 

 of the same kind of powder, which fell on a vessel a few hundred miles north- 

 ward of the Cape Verde Islands. Five parcels were sent to Dr. Ehrenberg for 

 examination, who found it to consist chiefly of the flinty cases of Infusoria, and 

 the siliceous tissue of plants. No less than sixty-seven distinct kinds of animal- 

 cules were detected, of which, sixty-four were fresh-water species, and the 

 remaining, two marine. 



The same observer, upon investigation, met with fifteen accounts of dust falling 

 upon vessels when far out on the Atlantic, off the coast of Africa. It has been 

 here known to descend upon the decks of ships, at the distance of several hun- 

 dred and even a thousand miles from shore, and when land was distant to the 

 north and south, full sixteen hundred miles. The dust is distributed thickly 

 through the air, soiling everything on board, injuring the eyes, and rendering the 

 atmosphere so hazy that vessels have been known to run ashore in consequence 

 of the obscurity thus produced. This dust is believed to come from the African 

 continent, from the fact that it occurs when the wind is from that direction, and 

 at the same time that the harmattan prevails, which is a periodical wind that 

 blows from the interior of Africa towards the Atlantic. Clouds of the finer par- 

 ticles of sand, from the arid deserts of this continent, are borne aloft by the 

 sweep of the harmattan, and carried far out over the sea upon the higher cur- 

 rents of the atmosphere. At the distance of three hundred miles from land, 

 Darwin discovered, in the fallen dust, particles of stone the thousandth part of 

 an inch square, mixed with matter still finer. 



In reflecting upon the facts just adduced, we see, that in order to become 

 acquainted with the structure of the world we inhabit, it is not sufficient to trust 

 to our unassisted vision. Wonders, and problems the most curious and interesting 

 will meet the gaze of the naturalist at every step he takes ; but unless he ex- 

 plores the secrets of nature with the magic glass of the microscope, half of the 

 treasures of truth will be still unrevealed : sealed from his vision by impenetrable 

 darkness. 



