VOLCANO OF RUCU-PICHINCHA. 25 



have reached immense distances, while violent earthquakes must 

 have desolated the neighbouring country. Had these been witnessed 

 by man, tradition ought to have preserved the memory of them. But 

 according to the historian of Quito, previous to the eruption of 1539, 

 Pichincha was not known to be volcanic ; the traditions of the In- 

 dians being absolutely silent on the point. The authors think it 

 therefore probable that the eruptions which caused the present cra- 

 ters took place before man inhabited this part of the Cordilleras. 

 The fumerolles of the present cone must also have been obstructed 

 during a great lapse of time ; otherwise the Indians must have no- 

 ticed great columns of smoke, such as now rise from it. The only 

 known eruptions in 1539, 1577? 1587 and 1660 have all issued from 

 the existing cone ; and to this epoch must be referred the blowing 

 away of the matter which choked the old vent, and the formation of 

 the present cavities. 



But in spite of history and tradition, it is impossible to believe 

 that the vast blocks, more than 12 ft. in diameter, which cover part 

 of the plain of Ina Quito, distant 3^ leagues, can have been thrown 

 out by the eruption of 1539. There are no traces of such recent 

 eruptions on the sides of Pichincha, and the present cone is far from 

 being considerable enough to have furnished such a vast quantity of 

 projectiles. Those which were thrown at angles less than 45° would 

 strike against the inner walls of the crater, and roll back again into 

 it ; those only which were thrown at greater angles, and with force 

 enough to rise 16,000ft. above the plain of Quito, could reach their 

 present positions ; and though this is not physically impossible, yet 

 it is contradicted by the appearances of the later eruptions, which 

 have clearly been of a very tranquil description. 



The authors consider as equally fabulous a tradition, that the erup- 

 tion of 1660 was accompanied by showers of incandescent rocks, 

 which are said to have fallen on all sides, but of which not a vestige 

 is now to be seen. 



J. C. M. 



Ehrenberg on the Sirocco-dust that fell at Genoa on the IQth 



May, 1846. 

 [From the * Berlin Monats-Bericht ' for 1846, p. 202-207.] 

 The microscopic analysis of this dust produced 22 polygastrica, 

 21 phytolitharia, together with the pollen of plants and the spores of 

 Puccinium. Tlie varieties of dust which since 1830 have fallen in 

 the Atlantic Ocean, as far as 800 sea miles west from Africa, on the 

 Cape Verd islands, even in Malta and Genoa, which the author has 

 had an opportunity of examining, all agreed in the following par- 

 ticulars : — 1st, they are all ochre yellow, never grey, like the dust of 

 the Khamseen in the north of Africa ; 2nd, the colour is produced by 

 iron oxide ; 3rd, from one-sixth to one-third of their mass consists 

 of recognizable organic parts ; 4th, these are either siliceous poly- 

 gastrica and phytolitharia, or carbonaceous but uncarbonized por- 



d2 



