BY H. I. JENSEN. 541 



House Mountain pantellarites. This rock intrudes Silurian slate, 

 and is therefore Post-Silurian, but there seems to be no reason 

 why it may not be as recent as the early Tertiary — the time of 

 volcanic activity in the New Hebrides. 



At Easter Eildon Hill* near Melrose, and at Mynydd Mawr, 

 Wales,! occur riebeckite trachytes supposed to be of Palaeozoic 

 age. 



(k) The Azore lavas, also Tertiary, and overlying a remnant of 

 Atlantis. 



(1) A very important mass of alkaline rocks (largely phonolites) 

 is found in the subsidence-areas of Franconia and Schwabia 

 immediately west of the Bohemian massive, between Thiiringer- 

 wald and the Harz Mountains. The subsidence-areas preserve 

 Jurassic and Triassic rocks deposited during transgressions of the 

 sea in Mesozoic times. These sedimentary strata are split into 

 thousands of fragments by step-faults between the Harz Mountains 

 and the Neckar. At Hogbau in Wiirtemberg there is in this 

 subsided plateau a subsidence-area with radial and peripheral 

 fractures through which phonolitic lavas and tuffs have been 

 emitted. The fracturing is mainly of Tertiary age. 



B. Asia. 



This continent not having undergone any thorough geological 

 exploration, has not yet furnished many examples of rocks of 

 foyaitic magma. 



In Armenia great eruptions took place in Eocene times, and 

 many of the lavas expelled were trachytes. Here again lavas of 

 alkaline character were expelled along the faulted flank of the 

 great Eurasian fold-axis. (Suess, Vol. i. fig.82. The mountains of 

 Armenia are situated on the line of ' Effondrements recents de la 

 Mediterranee' and on the ' Limite septentrional du l er Etage 

 Mediterranean '). 



* Harker's Petrology, 

 t * On the Occurrence of Riebeckite ' in Britain by Prof. Grenville A. J. 

 Cole. Min. Mag. Vol.ix. p. 219. 



