324 University of California Publications in Geology [Vol.11 



equivalents of the blue muds and that the cherts were formed in 

 water of only moderate depth, though probably at some distance from 

 the shore. 



IRELAND 



The lower Llandeilo of eastern Ireland contains radiolarian cherts 

 associated with tuffs and pillow lavas. 



In the Arenig rocks of Ireland, in Tyrone County, ellipsoidal lavas 

 are found associated with jaspers, 68 that do not appear to contain 

 radiolaria. 



The special feature of interest in this Irish area is the remarkable develop- 

 ment of volcanic materials which is there to be seen, spreading over a far wider 

 area than in Scotland. The rocks include lavas associated with tuffs and agglom- 

 erates, likewise a varied series of intrusive masses. . . . 



One of the most conspicuous features in some of these lavas is the occurrence 

 of the same sack-like or pillow-shaped structure which has been already referred 

 to as so marked among the Arenig lavas of Scotland. . . . 



These greenish lavas are occasionally interleaved with gray flinty mud-stones, 

 cherts, and red jaspers, which are more particularly developed immediately above. 

 In lithologieal character, and in their relation to the diabases, these siliceous 

 rocks bear the closest resemblance to those of Arenig age in Scotland. But no 

 recognizable radiolaria have yet been detected in them. 



URAL MOUNTAINS 



Radiolarian cherts are known in the lower Devonian of the south 

 Urals in the region around Orsk. 09 



These cherts occur in association with graywacke and are also 

 associated with greenstone and serpentine. Sometimes they are inter- 

 calated with tuffs. In one section described by Rose (p. 191) the 

 greenstone is described as being separated into ball-like masses. 



The cherts contain abundant radiolaria and manganese ores occur 

 in them. 



Specimens of red radiolarian chert, in the collection of the Uni- 

 versity of California, brought from the Ural Mountains by Professor 

 Lawson, are lithologically identical with the red chert of the Fran- 

 ciscan group. Professor Lawson 70 states that their appearance in the 

 field is identical with that of the Franciscan cherts. 



68 Geikie, A., Ancient Volcanoes of Great Britain, vol. 1, pp. 240, 244, Lon- 

 don, 1897. 



69 Gustav Rose, Mineralogisch-geognostische Reise nach dem Ural dem Altai 

 und dem Kaspischen Meere, Bd. 2, Berlin, 1842. 



Murchison, R. I., The Geology of Russia in Europe and the Ural Mountains, 

 London, 1845. 



Rust, Beitrage zur Kenntniss der fossilen Radiolarian aus Gesteinen der 

 Trias und der palaeozoischen Schichten. Palaeontographica, xxxviii, 110, 1891-92. 

 Guide des excursions du viieme Cong. geol. inter., St. Petersburg, 1897. 



70 Oral communication. 



