90 Correspondence — C. Callaway. 



by my friend Mr. Tuckett was not in granite but (as described by 

 myself on p. 12 of last year's volume) in a rock which was more 

 nearly allied to the pyroxenites and bore every appearance of 

 having had the structure completely altered by pressure, which 

 should have destroyed any pre-existent cavities. Thus, though 

 deeming myself fortunate in having elicited such an interesting 

 contribution to the discussion, I do not yet see my way to adopting 

 his explanation of the difficulty. T. G. Bonney. 



THE EASTERN GNEISSES OF THE SCOTTISH HIGHLANDS. 

 SiK, — Mr. G. Barrow's paper on the Moine Gneisses of the 

 Highlands (Quart. Journ. Geol. Soc, November, 1904) revives 

 memories of old controversies. In 1883 I gave reasons (Q.J.G.S., 

 pp. 355-4:14) for believing that the thin-bedded gneisses east of the 

 line of the great overthrust were older than the Assynt Series (now 

 proved to be Cambrian), and I proposed to call them 'Caledonian.' 

 Professor Lapworth's brilliant work on the dynamo-metamorphism 

 of the Highland region quickly followed, and it suggested the 

 possibility that the Eastern Gneiss was a melange of rocks of 

 different kinds and ages which had been rolled out in the earth- 

 mill. However, the researches of the Geological Survey seem to 

 have rehabilitated my original contention, since they lead to the 

 conclusion that these gneisses, in the words of Dr. Home, "repre- 

 sent sediments of siliceous and argillaceous type." Sir A. Geikie 

 in 1891 proposed the name ' Dalradian ' for the gneisses and 

 associated rocks of the southern Highlands ; but these ai"e now 

 correlated by the Survey with the Moine Gneisses of the north- 

 west, that is, with my Caledonian. I held that these rocks were 

 pre-Cambrian, but newer than the Hebridean ; and this, I under- 

 stand, is the view which Dr. Home is disposed to adopt, when, in 

 the debate on Mr. Barrow's paper, he points out resemblances 

 between them and the pre-Torridonian schist north of Loch Maree. 

 If therefore any name is to be given to these eastern gneisses, 

 I respectfully submit that 'Caledonian' has priority over 'Dalradian.' 



Mr. Barrow's memoir suggests another point. In my papers on 

 the "Crystalline Kocks of Malvern" (1887-1893), I contend that 

 black mica is produced from chlorite. This view was received 

 with opposition. The peaceful pages of the Geological Magazine 

 resounded with the weighty artillery of the late Lieut.-General 

 McMahon thundering against "The Rape of the Chlorites." I de- 

 clined to surrender, and now I am supported by Mr. Barrow, who 

 remarks (p. 414) that " A striking feature of the grey gneisses is 

 seen in the films of felted biotite, derived from original clastic 

 chlorite , ..." If chlorite is changed to biotite in Scotland, 

 why not at Malvern, where too the associated acidic and basic rocks 

 readily account for the necessary potash and iron-oxide ? Since my 

 heresy receives such respectable support it would seem to be worthy 

 of reconsideration. C. Callaway. 



Cheltenham. 



December 27th, 1904. 



