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PBOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Feb. 6, 



of these masses preserve the normal strike of N.E. and S.W., with 

 considerable deviations, however, to the N. and S. of E., there are 

 examples of east and west directions ; and we meet with others 

 (particnlarly high np the Tilt, between the Cloehan and the Tarn) 

 where the strata striking from S.E. to N.W. are there placed at 

 right angles to the direction of the normal masses. This takes place 

 where intervening syerritic and granitic rocks occur, the stratified 

 rocks being arranged with divergent strikes and dip around snch 

 amorphous bosses. 



In fact, it is sufficient to ascend the Banavie Burn from the Castle 

 of Blair for half a mile to see every possible discordant break among 

 strata of limestones and schists which have been penetrated by 

 porphyritic and syenitic rocks. 



We do not pretend to have succeeded in unraveling the geolo- 

 gical structure of this most difficult and intricate region. There 

 are probably some powerful faults, whereby parts of the series are 

 repeated, while other portions are concealed from view ; but we 

 could not satisfy ourselves as to the exact position of any one 

 dislocation. Besides faults, however, the district is greatly compli- 

 cated by the curvings and twistings of the beds, so carefully and 

 completely investigated by Playfair and Webb Seymour*, and by 

 Maccullocht. 



We are unable to decide what relation the limestone of Loch Ban- 

 noch and Glen Erochie bears to that of Inverveck — the point where 

 limestone is first seen in descending the Garry. If we could suc- 

 ceed in identifying them, probably a great part of our difficulty 

 would be removed. The rock at Inverveck on the south-west side 

 of the Garry, 2| miles from Blair- Atholl, is a white, grey, or green- 

 ish crystalline rock, sometimes almost a steatite, with pale leek- 

 green, talcose laminas. The strata are much broken, but the dip is 

 on the whole south-easterly. 



In the grounds of the Ditke of Atholl, espcciaUy along the 

 classic Glen Tilt, good sections are obtained of parts of this lime- 

 stone series, traversed by veins of granite and porphyry. There is 

 much local disturbance and great metamorphism at this locality. 

 Nowhere can this be better seen than in the deep wooded dell of 

 Glen Banavie, immediately behind Blair Castle. We first encounter 

 dark schists, greatly hardened and traversed by dykes of felspar- 

 porphyry, which have a N.N.E. strike. The strata have here no 

 determinate dip ; indeed, the bedding is almost obliterated. Higher 

 up, however, the disturbance lessens ; and eventually the usual flag- 

 stones set in, with a steady south-easterly dip at 25° or 30°. 



* Trans. Eoy. Soc. Edinburgh, vol. vii. p. 303. 



t Trans. Geol. Soc. vol. iii. See especially Macculloch's admirable descrip- 

 tion of Glen Tilt (foe. cif. p. 297). He speaks of granite having a foliated 

 structure, and of that structure being especially observable in the vicinity of 

 quartz-rock. He dwells particularly on the distinction between quartz-rock'and 

 gneiss (p. 294), and shows that in Glen Tilt the general series consists of mica- 

 slate alternating in a very irregular manner with hard argillaceous schist and 

 quartz-rock, and with a few beds of limestone (p. 291). The syenite and green- 

 stone of Playfair and Webb Seymour are called by him granite. 



