90 Krug von Nidda on the Mineral Springs of Iceland. 



gains probability, the more necessary it becomes to separate, by 

 strict and severe examination, facts from opinions, a task which 

 is not the work of a few days ; and it is also the more necessary 

 to avoid enveloping the facts in mystery, and to limit them, by 

 careful investigation, to the boundaries which may be reached 

 with probability, and which Nature herself has indicated. 



We may regard as fully ascertained facts, that the following 

 substances consist, either entirely or in part, of the shells of lori- 

 cated infusoria, viz. 



1. Bergmehl, \ Of the newes t formation. 



2. Kieselguhr, } 



3. Polishing slate, ") 



4. SaugscUefer, > Tertiary substances. 



5. The semi-opals of the polishing slate, J 



We may consider the following minerals as 'very probably of 

 the same description : 



6. The semi-opal occurring in Dolerite, 



7. The precious opal occurring in porphyry, 



8. The flints occurring in chalk, 



9. Yellow earth, 1 ^f?*.i_ 



V Of the newest formation. 



10. Bog iron-ore, J 



11. Certain kinds of lithomarge.* 



\ 



I 



J 



On the Mineral Springs of Iceland. By C. KRUG VON 



NlDDA.-|- 



AFTER having spent some days in the vicinity of Hecla, and 

 having, on the 3d August 1833, ascended that mountain, I pur- 

 sued my journey towards the hot springs of Haukadal, under 

 which are included the great Geyser and the Strokr. These 



* The examination of a boulder found in the Mark Brandenburg, which had 

 been regarded as a floatstone or Schwimmstein (Quarz-agathe nectique, H.), 

 has recently proved to me, that its principal mass consists of unattached sili- 

 ceous spicula of sponges, and of the small globular bodies (infusoria, Pyxidi- 

 culis ?) which the flint pebbles of the district contain in great abundance. 

 These bodies occur in the powder of the flinty envelope. The Schwimmstein^ 

 therefore, bears the same relation to the flint as the polishing slate to the 

 semi-opal, and it is to be referred to the chalk. 



f From Karsten's Archiv. vol. 9, p. 247. 



