348 



tablets of tridymite. Under the microscope biotito, magnetite, epidote 

 and apatite may also be recognized as occurring in certain specimens 

 of the rock. The ground-mass is crowded with minute grains of 

 magnetite and indefinite granular matter. According to VON LASAULX 

 it may be resolved, under a high power, into a confused aggregate of 

 felspar-microlites and quartz-grains. Specimens examined by the 

 author cannot, be resolved. The matrix can only be described as 

 crypto-crystalline. The large quartz grains show the corroded forms 

 characteristic of the liparites and quartz-porphyries. 



Cleavage flakes of the sanidine parallel to (010) give an extinction 

 of 11 referred to the edge 010 : 001. The optic axial plane is at 

 right angles to the plane of symmetry (orthose non deforme). 

 The optic axial angle (in air) for red light was determined by VON 

 LASAULX to be 28|. Mr. DICK observed an angle of 46 in a 

 specimen isolated by the author. The rock was analysed by Mr. 

 HARDMAN/ 1 ) but his analysis is so exceptional as regards the amount 

 of alumina and lime that another analysis was kindly made for the 

 author by Mr. PLAYER. It agrees with that of Mr. HARDMAN except 

 as regards the alumina and lime. 



I. II. 



Si0 2 ... 76-4 ... 64-66 



AL,0 S 14-2) 



Fe 2 o 3 ... i-el 2 - B 



CaO ... -6 ... 1-21 



MgO 



K 2 ... 4-2 ... 8-61 



Na 2 ... 1-8 ... 5-44 



ELO 1-5 



100-3 99-95 



I. Liparite ; Tardree (PLATER). 

 II. Sanidine from the liparite (Dr. BETTENDORF).^) 



Felsites and porphyritic felsites are associated with the Lower 

 Palseozoic rocks of Wicklow and Waterford, and with the Old Red 

 Sandstone rocks of Kerry. They are the siliceo-felspathic rocks of 

 Dr. HAUGHTON. Porphyritic constituents are not conspicuous in these 

 rocks. They resemble the Ordovician felsites of Wales in structure 

 and composition. 



A banded spherulitic felsite occurs at Knockanduff, Co. Waterford. 

 The spherulitic bodies may or may not show radial structure. In the 



(1) Jour. G-eol. Soc., Ireland, XIII., 29. Mr. HARDMAN'S analysis is as follows : 



Si0 2 , 76-960; A1 2 3 , 5-101; Fe 2 O 3 , 2-344; CaO, 7-064; MgO, 0- 295 ; K 3 0, 4-262 ; NaoO, 

 1-818; H 2 0, 2-102; P 2 3 , Trace. 



It is interesting to observe that Mr. PLAYER'S analysis agrees exactly with Mr. HARDMAN'S 

 so far as the alkalies are concerned. 



(2) VON LASAULX. T.M.M., Neue Folge. Band I. (1878), p. 417. 



