lii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



exhibits a multitude of small longitudinal and parallel ravines, having 

 often a depth of 5 or 6 metres (16^ to 19^ feet). The centre of the 

 stream still, in July 1846, contained numerous fumeroles in which 

 were beautiful transparent crystals of muriate of ammonia, and large 

 fibrous masses of the same salt, together with a vast quantity of mu- 

 riate of iron." The rugged surface here described is, as you are aware, 

 a very usual accompaniment of lava streams, arising from the cooling 

 and subsequent cracking by the heat of the inferior fluid mass, and 

 beneath this fissured crust there might be a continuous stream of 

 homogeneous lava, which in cooling would become columnar, and a 

 cross section of the stream would in that case probably exhibit a mass 

 of basaltic pillars, capped by an amorphous layer, and that surmounted 

 by a congeries of blocks, the fissured surface of the stream, just as we 

 see numerous instances in Auvergne, and in many districts where the 

 older trap rocks have flowed in broad streams. M. Elie de Beaumont, 

 in his very elaborate and interesting researches on the structure and 

 origin of Etna, maintains that, in accordance with M. Von Buch's 

 theory of craters of elevation, the beds composing the nucleus of the 

 central mass of Etna have been raised to their present inclination, from 

 a position approaching nearly to horizontality ; and appears to be of 

 opinion that no homogeneous stream of lava could consolidate into 

 stone on a surface having an inclination of more than 7 or 8 degrees*. 

 M. Descloizeaux states, as already mentioned, that in some places 

 the stream from Hecla has an inclination of as much as 25 degrees ; 

 but if the parts so inclined are composed only of blocks and scoriae, if 

 underneath there be not abed of homogeneous lava, that amount of in- 

 clination would not be opposed to the theory of M. Elie de Beaumont. 

 We must hope that the detailed descriptions of the French and German 

 observers will throw much light on the structure of this vast expan- 

 sion of melted stone. I understand that M. Waltershausen is one of 

 those who went from Germany, and his seven years' study of Etna 

 renders him peculiarly qualified to describe the phsenomena and com- 

 pare them with those with which he is so well acquainted. 



In the Proceedings of the Royal Academy of Berlin for December 

 184'5, there is an account of a paper read by Professor Ehrenberg, 

 containing the result of a microscopic examination of the dust that 

 fell on the Danish vessel ; and in the Proceedings for May last there 

 is a supplement to that paper, describing his examination of some 

 ashes that had been erupted from Hecla on the day above-mentioned. 

 Translations of these notices are given in the last number of the 

 Quarterly Journal of this Society. In these notices, Professor Ehren- 

 berg identifies the dust that fell on the ship with the ashes erupted 

 from Hecla, and they afford another instance of that very remarkable 

 fact, previously made known to us by the same philosopher, viz. the 

 presence of the siliceous shells of infusoria in ashes ejected from vol- 

 canos in many different countries. He found thirty-seven different 

 species of these minute organisms, not one of them decidedly new, 

 and all of them peculiar to fresh water. Fifteen are living forms 

 known to exist at present in Iceland. 



* Description Geologique de la France, tome iv. p. 176. 



