Intelligence and Miscellaneous Articles. 67 



intermixture of species, notwithstanding the irregular repetition of 

 the zones, the non-occurrence of these colony species in interme- 

 diate beds, and other reasons. The stratigraphy and palaeontology 

 of several of these colonies was discussed in detail, showing it to be 

 more probable that their apparent intercalation with later faunas 

 is due to repetition by faulting. 



3. " On the Pre-Cambrian Eocks of the North-western and 

 Central Highlands of Scotland " By Henry Hicks, Esq., M.D., 

 E.G.S. 



The author, after examination, considers the rocks of the fol- 

 lowing districts to be wholly or in part Pre-Cambrian : — 



(1) Glen Finnan, Loch Shiel to Caledonian Canal. — In the former 

 district the rocks are gneiss, often massive. In Glen Firmilee is a 

 series which the author regards as newer and Pebidian. At Earo- 

 fern are quartz rocks which the author identifies with those beneath 

 the limestone in Glen Laggan, near Loch Maree, and probably of 

 Silurian age. At Bannavie is a granite which the author considers 

 to be Pre-Cambrian. 



(2) Fort William and Glen Nevis. — In this district chloritic 

 schists and gneiss occur, which the author regards as Pebidian. 



(3) Ballachulish, Glen Coe, and Black Mount. — Chloritic schists 

 and quartzites occur here, followed near Loch Leven unconformably 

 by Silurian rocks. On the east of the Ardsheal peninsula there is 

 granite which the author believes to be Pre-Cambrian. Going eastward 

 from Ballachulish we have slates, probably of Silurian age. In Glen- 

 coe are granite-banded f elsite, gneiss, breccia, resembling as a whole 

 the rocks of the "Welsh xlrvonian group. Between the Black Mount 

 and Loch Sullich are traces of a great Pre-Cambrian axis, bringing 

 up the gneissic series ; this is traceable also towards Glen Spean 

 and Loch Laggan to the N.E. 



(4) Tyndrwm to Callander. — South and east of the former are 

 gneisses and silvery mica-schists. Crystalline limestones and ser- 

 pentines are associated near Loch Tay, resembling those in the 

 Pebidian series of North Wales. 



The author states that the Silurian (and Cambrian) rocks flank 

 the Pre-Cambrian in lines from N.E. to S.W., and overlap Ben Ledi 

 on the south side. Thus here, as elsewhere, subsequent denudation 

 has removed enormous masses of the more recent rocks, only here 

 and there leaving patches of these in folds along depressions in the 

 old Pre-Cambrian floor. 



XL Intelligence and Miscellaneous Articles. 



NOTE ON THE CONDUCTIVITY OF TOURMALINE CRYSTALS. 



BY GEORGE FRANCIS FITZGERALD, M.A., F.T.C.D. 



TN the Philosophical Magazine for July 1879, Professor Sylvanus 



-*- Thompson and Dr. Oliver Lodge give the results of some very 



interesting experiments upon the unilateral conductivity of tour- 



