Hyland — On some Spherulitic Rocks from Co. Down. 427 



little granular sphene is to be observed. Oxides of iron are 

 infrequent. The occurrence of prismatic apatite could also be 

 established. 



The specific gravity of the rocks varies. Three estimations 

 gave 2-586, 2-595, 2-605 at a temperature of 20° 0. The mean 

 sp. g. is therefore 2 - 589. The variation is presumably due to 

 the fact that the amount of free quartz varies in each speci- 

 men. The SiOa is not a constant quantity. It was found upon 

 estimation of portions taken from different hand specimens to vary 

 from a little under 74 °/ to 70 °/ o . Two complete analyses of the 

 rock were executed. 



Under I. and II. are given two analyses of the rock from near 

 Newcastle. 



Under III. the mean. 



Under IV. Liparite (Quartz-Trachyte) from the Chiaja di 

 Luna, Ponza Island. 1 



Under V. an analysis furnished by Peach and Home of the 

 spherulitic felsite from Papa Stour, Shetland Isles. Of the micro- 

 scopic characters of this rock the authors say : — 



" Instead of presenting a marked crystalline aspect, it shows a felsitic 

 groundmass ... in which few felspar crystals are discernible. . . . The 

 characteristic feature of the rock is the well-marked spherulitic structure 

 which it presents under the microscope. . . . We are inclined to believe 

 that the felsite originally possessed a vitreous character, which has, to a 

 large extent, disappeared through devitrification." 2 



Under VI. " Claystone," Arran, analysis by M. M. Tait, 

 quoted from Bryce's " Geology of Arran," p. 203. 3 The rock is 

 presumably a felsite. 



Under VII. Felsite-porphyry with spherulites from Felsen- 

 keller, near Ilmenau in Thuringia. 4 



1 Kalkowsky, Elemente der Lithologie : Heidelberg, 1886, p. 75. 



2 The old Eed Volcanic Eocks of Shetland: Transactions of the Eoy. Soc. of Edin- 

 burgh, vol. xxxii. Part ii., p. 383 (1884). 



3 Teall, British Petrography, p. 347. 



4 E. Kalkowsky, Op. cit. p. 68. 



