Dr Brewster on Oxahverite. 115 



cle west of the true sun was more bright than the rest, the 

 extreme north and south points of the two largest circles were 

 very dim, and the eastern extremity of the small circle some- 

 what flattened. In this halo, the two circles mn, np of Fig. 

 S are completed, and there are additional segments at D D. 

 In this halo, the circle of which A is the centre is less than 

 that in Fig. 3, where there are also parhelia not seen in the 

 other. 



On the 14th August 1825, there was seen at Millbury, 

 Massachussets, the halo shown in Plate I. Fig. 6. It was seen 

 at eight o** clock in the morning, and continued till past eleven. 

 S is the sun, A B a circle having the sun in its centre and 

 about the size of the common halo. C D an ellipsis, and E F 

 a large circle at the west of the sun through which its circum- 

 ference passed. The colours, except at the points G H, were 

 like those of the rainbow. 



Art. XXIII, — Description of Oxahverite^ a New Mineral 

 from Oxahver^ in Iceland. * By David Brewster, LL. D. 

 F. R. S. Lond. and Sec. R. S. Edin. 



The very interesting mineral which I now propose to de- 

 scribe was put into my hands by Henry Witham, Esq. whose 

 knowledge of mineralogy and zeal for its progress are already 

 well known to the society. 



The specimens on which it is found were brought from the 

 hot spring of Oxahver, in the north east of Iceland, by Mr 

 Brown of this city. They are decided petrifactions, in which 

 the wood has been replaced by calcareous spar of a fine ochre- 

 yellow colour, and more or less crystallized. This opinion 

 was doubted by competent judges who had seen some of the 

 specimens, but I consider it as completely established by a 

 specimen now upon the table, which, along with some others, 

 Mr W. G. Thomson has been so kind as to send me from his 

 cabinet. 



The new mineral occurs on these petrified masses in thin 

 veins, in amorphous masses, in aggregated groups of crystals, 



' * Communicated to the Royal Society, May 7, 1827. 



