10 GEOLOGICAL MEMOIRS. 



which fossil species are distributed in the various formations of 



different districts." 



The author concludes the work we have been analysing with a 



tabular statement of the classification of these secondary rocks, and 



with a comparison of the Jura-liassic formations of Lombardy with 



those of the Monti Pisani. _^,_ _. ^-. _ 



[ W. J. Hamixton.J 



Memoirs on Meteoric Dust and Volcanic Products from Hecla con- 

 taining Organic Bodies, By Professor Ehrenberg. 



[From the * Bericht viber die Verhandlungen der K. P. Akademie zu Berlin.'] 



1 . Investigations with regard to Meteoric Dust that fell in the Ork- 

 ney Islands on the 2nd of September 1 845, and on the Volcanic 

 Products erupted on the same day from Iceland^ and the admixture 

 of Microscopic Organic Bodies with these substances. (Berlin 

 ' Bericht' for Dec. 1845, p. 398.) 



In October last Professor Forchhammer of Copenhagen forwarded 

 a specimen of dust which fell on board the Danish ship Helena, on 

 the 2nd of September, at nine o'clock in the evening, while in lati- 

 tude 61° N. and longitude 7° 58' W. of Greenwich*. This speci- 

 men was submitted by the author to microscopic investigation. 



The dust was of a greenish black-brown colour, not unlike that of 

 much-roasted coffee when ground ; its particles were less adherent 

 to one another than is the case with meal or coal-dust, rather re- 

 sembling fine dry sand ; it was easily blown away, felt somewhat harsh 

 when rubbed by the finger on smooth paper, and was decidedly 

 gritty between the teeth. 



The microscope at once showed that the substance was not a 

 vegetable ash ; its particles were on the contrary irregular, often 

 angular, indented and channelled little bodies resembling pounded 

 or scraped pumice, and by transmitted light exhibiting the colour 

 of brown bottle-glass or obsidian. 



Amongst the fragments unquestionably inorganic and resembling 

 pounded glass were soon recognized some distinct siliceous organic 

 bodies, and especially the almost perfectly preserved shells or cases 

 of an infusoria, Navicula silicula. By degrees also were recognized 

 fragments of six other known organic forms. 



Upon the discovery of these the investigations were extended, 

 both with regard to the substance itself under examination and also 

 its relations with corresponding phsenomena, especially with refer- 

 ence to the meteoric dust of the Cape de Verd Islands and the vol- 

 canic deposits of the Eifel. 



* A thick cloud with strong wind (not a storm) from N.W. by W. was seen to 

 approach the vessel, and the ship and sails were covered with ashes. On the 

 same day took place the eruption of Hecla, distant 115 German miles (533 En- 

 glish). According to Prof. Forchhammer, the cloud of ashes must have been 

 driven at the rate of 10 German miles (46 EngHsh) per hour. 



