HAUER ERUPTION AT SANTORINO. 21 



The results obtained are : — 



A. B. C. 



Density (small pieces at 18° C.) 2-566 2-544 2-507 



Silica 67-05 67-25 68-12 



Alumina 15-491 oq.nQ [14-52 



Osydulated iron 5-77/ ^^ ^^ 15-73 



Lime 3-41 3-36 368 



Magnesia 0-77 070 0-64 



Potash 2-341 .... r2-23 



Soda 4-65/ "^^^ 14-96 



Loss by incandescence 047 55 43 



99-94 (sec) 10000 100-31 



The iron is calculated as oxydule ; but a part of it is certainly 

 oxydo-oxydule, all the specimens analyzed acting on the magnetic 

 needle, while another part has been changed into oxide in con- 

 sequence of decomposition. The analytic results prove these speci- 

 mens to be identical with the lavas of the last eruption. 



A specimen of older eruptive rocks from Santorino (D) was of 

 different composition, containing a less proportion of silica and a 

 greater of basic substances than the lavas of the present eruption 

 (A, B, & C). It is very compact and hard, with an uneven fracture, 

 and varying between dark grey and black. It is rather equally in- 

 terspersed with small concretions of granular olivine and white 

 vitreous felspar. The first of these two minerals is more or less 

 decomposed, with superficial reddish and brownish tints. Magnetic 

 oxide of iron, although scarcely visible, must be disseminated 

 through the whole rock, as it possesses a rather notable amount of 

 magnetic power. The presence of hornblende and augite could not 

 be ascertained. A specimen of white and very light pumice (E) 

 was collected near the bathing-houses of Nea Kaimeni. 

 The analytic results are : — 



D E 



Density 2-801 — '- 



Silica 55-16 60-09 



Alumina 15-94 13-14 



Oxydulated iron 9561 6-34 



Lime 8-90 2-95 



Magnesia 510 046 



Potash 1-45 4-39 



Soda 3-21 6-00 



Loss by incandescence 1-07 5*41 



100-39 98-78 



Heated in a retort, the pumice (E) emits water, hydrochloric 

 acid, and chloride of ammonium, without any trace of sulphuiic 

 acid. Like D, it is but slightly attacked by acids, and fuses easily 

 into a black pitchstone-like slag. 



The general result is, that the whole of the substances ejected by 

 volcanic eruption in the Bay of Santorino are nearly related to the 

 pyroxenic andesites. The rocks enumerated under this designation 

 by Mr. Roth generally contain between 55 and 67 per cent, of silica ; 



* Calculated from the loss of weight. 



t Together with some oxide and oxydo-oxydule ; no trace of manganese. 



f2 



