235 



iserious omission is siilphur ; but though the rocks occur in 

 mineral-bearing country no sulphides were visible in them. 



With regard to the granophyric gabbro-diabase from 

 one mile west of Blinman, an interesting possibility is sug- 

 gested by a paper by G. W. Tyrrell on ''The Petrology of 

 the Intrusions of Kelsyth-Croy" (6) (Scotland), which came 

 to hand just after my work for this paper had been completed. 

 The rocks he describes are diabases occurring in dykes and 

 laccolites, and have a granophyric base exactly similar to 

 many carboniferous diabases in England. In endeavouring 

 to account for this peculiar characteristic, the author finds 

 that similar rocks are of world-wide distribution, occurring 

 always in sills, laccolites, or dykes, intruding acid sediments 

 •or gneisses, and are often connected with normal basalts and 

 diabases as products of the same magma. Further, the chem- 

 ical composition of the granophyric rocks is remarkably con- 

 stant, as may be seen from the following table : — 



■ 



1 

 A 



B C 



D 



E 



F 



Si 0-2 



52-68 



51-19 53-26 



51-15 



49-80 



50-55 



Al^O, 



14-14 



15-80 1 15-64 



15-92 



17-77 



15-00 



Fe, O3 ... 



1-95 



3-08 



•24 



9-34* 



2-29 



2-54 



Fe 



9-79 



11-20 



7-44 



2-87* 



8-75 



7-90 



MnO 



-44 



trace 



■11 



-09 



trace 



— 



MgO 



6-38 



5-63 1 8-64 



6-48 



5-67 



6^25 



Ca 



9-38 



9-58 1 12-08 



10-40 



8-85 



7^85 



Na, 



2-56 



2-09 ' 1-25 



1-19 



1-48 



3-53 



K, 



-87 



-60 ! -58 



1-61 



•48 



110 



H, 



1-60 



-30 ! -76 



•11 



3-66 



3-69 



Ti 0, 



— 



-40 



•70 



-44 



1-56 



1-58 



C 0, 



— 



nil 



-04 



— 



— 



- — 



P. 0, 



— 



•008 



— 



•06 



trace 



— 



FeSa 



— 



-005 — 



• — 



100-31 



— 



Totals ... 



99-79 



100-883 



100-74 



99-66 



99-99 



* Surely these figures have been transposed. 



A. Diabase, Mount Holyoke, Massachusetts. 



B. Diabase, dyke, Potaro River, British Guiana. 



'C Dolerite (with micropegmatite). Knob Head, South Victoria 

 Land, Antarctica. 



D. "Augite diorite with micropegmatit-e," Seven Pagodas, Ohin- 



gelput, India. 



E. Granophyric-diabase, Auchinstai-y, Kilsyth. 



F. Quartz-Gabbro, Cam Llidi, St. David's. 



(6)Geol. Mag., 1909, July, p. 299; August, p. 359. 



