3G8 M. Theodor Kjerulf on a 



even with the assistance of a lens, detect iron pyrites, with 

 anything like certainty, although that variety 2 exhibited 

 traces of sulphuric acid and spicula, resembling hydrous oxide 

 of iron. 



The materials for the investigations of which the results 

 are here communicated, were collected by myself on the spot, 

 during a journey to Iceland, in the summer of 1850, and the 

 analyses themselves, were conducted according to the method 

 followed by Professor Bunsen,and communicated by Dr Streng 

 (Bietrag zur Theorie der vulkanischen Gesteinsbildung, Bresl., 

 1852.) In the environs of the Baula, a mountain from which 

 so much instruction may be derived in regard to the trachyte 

 of Iceland, I could not, after the most careful search, discover 

 any of the quartziferous rocks. These I have observed only, 

 not under the most favourable circumstances for observation, 

 at Kalmanstunga in the western, and at Trollakirkja, in the 

 northern, parts of the island. At Kalmanstunga, at the de- 

 clivity of the mountain which stretches towards Koita, there 

 is an alternation of numberless A^arieties of trachyte, com- 

 pact, earthy, nodular, breccious ; and it is amongst the frag- 

 ments of the latter, that at the declivity in question, the 

 quartziferous porphyritic trachyte is found. The contiguous 

 rock and the junction of the two are, unfortunately, concealed 

 from observation by heaps of rubbish. As far as could be 

 recognised, the whole composed a veniform mass (eine stock 

 = oder gangformige masse), which might probably extend 

 over Tunga to the trachyte cliffs of the Nordlingafljot. It 

 should also be mentioned that the trachyte mountain in the 

 neighbourhood of the above-mentioned locality, lias been 

 broken through by a basaltic mass, which can be recognised 

 at a considerable distance by its beautiful columns. The 

 second variety subjected to analysis is from the northern dis- 

 trict of the island, where the road from Fagranes to the Ska- 

 gafjordr leads through the narrow valley of Vidadalr towards 

 Grimstungur. Right across the valley, where it stretches in 

 a southerly direction, there runs down from the mountain of 

 Trollakirkja a vein of quartziferous trachytic porphyry, but 

 here likewise the line of junction with the adjoining rock, 

 which was a common dark augitic and palagonitic rock dis- 



