12 GEOLOGICAL MEMOIRS. 



into fine powder, that no time or opportunity would be allowed fdr 

 them to be carbonized. '---: 



4. That the filaments of absorbent paper were the only things now 

 remaining to throw any doubt on the author's mind as to whether 

 the accurate investigations made with regard to them were of any 

 value, in consequence of the chance of impurity of the material in- 

 vestigated. 



The author therefore in October applied to M. Forchhammer, to 

 know if there were other ships or localities from which similar dust 

 could be obtained. He obtained in consequence three specimens of 

 the most recent volcanic products from Iceland itself. The first was 

 a specimen of volcanic ash " collected in the neighbourhood of the 

 volcano, and probably thrown out at the first powerful irruption of 

 ashes." The next was a piece of pumice, and the third a fragment 

 broken from red-hot lava. 



These specimens underwent careful investigation ; the second and 

 third exhibited no organic body, and no remarkable appearance 

 under the microscope, but the ashes were so singular that it appeared 

 to render the publication of the present investigation and that of the 

 Orkney dust a necessary duty on the part of the author. 



The specimen of ash in question is black, finely porous and light, 

 showing in a recent fracture a greenish grey coloui[' and vitreous 

 lustre. The broken surface exhibits many internal cells filled with 

 a clear brown earth, many also only thinly covered with this earth 

 on the walls of the cells. Some cells on the surface were similarly 

 filled. 



Microscopic investigation gave two remarkable results, which are 

 of great interest as placing beyond doubt the true nature of the 

 Orkney dust : — 



1. Fine dust scraped from the ashes showed exactly similar frag- 

 ments, both in colour and form, to those which make up the prin- 

 cipal mass of the meteoric dust of the Orkneys. 



2. The clear brown earth in the cells of the ashes abounds with 

 siliceous-shelled infusoria and phytolitharia. 



The following forms have been obtained from ten separate inves- 

 tigations, each consisting of about half a cubic line of this mass:— 



^,j , a. Siliceous-shelled Polygastrica. 



-v-.r 1. Eunotia zebra. 



"^f 2. Gomphonema minutissiraun]. 



'■''" 3. Pinnularia borealis. 



''^^ 4. P. (? another species.) 



sii- ' 



, b. Siliceous Phytolitharia. 



5. Lithostyhdium rude. 



These are all known freshwater species, with the exception of a 

 doubtful Pinnularia or Fragilaria. - 



Ar:. General Result and Conclusion. 



i. The fine brownish black vitreous dust which fell in the Orkneys 

 on the 2nd of September, and appeared as an advancing cloud, does 



