EHRENBERG ON METEORIC AND VOLCANIC DUST. 15 



1. How far are these ashes and ash deposits significant ? Are they 

 remarkable for extent or local thickness ? How far do they extend ? 

 How thick are they? 



2. How far from the crater are the thickest of these deposits, and 

 what is their thickness, whether by calculation or actual measurement? 



3. Do the finer ashes and the coarser ones, when erupted at the 

 same time, repose in alternate layers on one another, or are they se- 

 parated, falling at different distances from the crater? In what pro- 

 portions do they appear ? How are they affected by wind and rain 

 occurring at the time? 



4. Is it the case that much rain and storm occurs during the 

 whole time of eruptions, or has it only regularly accompanied the 

 more violent eruptions? 



5. How thick and to what an extent of surface may we estimate 

 the covering of vegetable mould immediately disturbed and affected 

 by the eruption ? 



6. Does it appear from the recollection of persons living near, 

 that there are or were, in the neighbourhood of active craters, any 

 hollows, pools or marshes, formerly filled with water, or turf and 

 vegetable mould (not with snow and ice only), which are now dried 

 up or seem to have disappeared ? If so, of what probable superficial 

 extent are they ? 



The author then in conclusion offers the following suggestions with 

 regard to collecting objects for investigation : — 



a. Dry ashes of all kinds that have not been wetted since they 

 were thrown out in a heated state, with an account of the probable 

 thickness of the heap, the superficial relations, and especially very 

 distinct information with regard to locality. 



b. Dust conveyed by the air immediately upon sails, on clean 

 linen spread expressly for the purpose, on plants, or on clean planks, 

 especial care being taken to avoid any possible admixture with 

 foreign bodies. 



c. It would be useful to have specimens taken from some depth 

 beneath the surface of thick recent deposits of ashes, together with 

 an account of their estimated thickness and extent. 



d. The fine ashes are quite as important for the inquiry as the 

 coarser ashes and the lapillse or slag. 



e. Small fragments of pumice of all the various kinds carefully 

 collected cannot fail to be interesting. 



f. With regard to the perfectly solid masses, slags and true lava, 

 the organic bodies have usually undergone so much change in them 

 as to be scarcely recognizable ; but when they are glassy or obsidian- 

 like, there is always some hope that imperfect fusion may have left 

 them in bubbles and cells, where are preserved some fragments that 

 can be made out. 



g. All specimens should be preserved in clean white writing-paper, 

 and not in grey absorbent paper, since the filaments readily worn off" 

 from the surface of the latter material by the rough substances con- 

 tained in them become mixed with the specimens and greatly im- 

 pair their value. [D. T. Ansted.] 



