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PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Feb. 6, 



/The cuttings of the Dunkeld Railway have shown the junction of 

 these slates with the overlying Old Red conglomerates. The slates 

 are there considerably twisted, and their edges are covered by a con- 

 glomerate, which consists mainly of felspathic matter, the pebbles 

 being for the most part rounded and subangular pieces of various 

 amygdaloidal and porphyritic felstones. It was evident at a glance 

 that these pebbles of igneous rock were not derived from the Gram- 

 pians, since they differed lithologically in a marked degree from 

 the felspathic rocks of the crystalline region. Another fact readily 

 observable was the great scarcity, in places the entire absence, of 

 any fragments of the metamorpbic rocks of the neighbouring moun- 

 tains, or even of the slates on which the beds of conglomerate rest. 

 The inference we formed was, that these conglomerates were derived 

 from volcanic ejections during part of the Lower Old Red Sand- 

 stone period ; and this was speedily confirmed by finding, inter- 

 stratified with the conglomerate, a band of dark compact amygdaloidal 

 felstone, above whicb the conglomerate became exceedingly coarse, 

 and contained large detached masses of this same felstone. The 

 strata become finer as they recede from the junction with the slates, 

 and to the south pass gradually upwards into sandstones. 



Spittal of Glenshee to Blairgowrie. — The last traverse which we 

 made this summer was from the Spittal of Glenshee, clown that glen, 

 to Blairgowrie and Dunkeld. From the Spittal a glen called Glen 

 Beg branches off to Braemar in a N.N.E. direction. Its western 

 side is formed by a line of limestone which also ranges south- 

 east for nearly a mile. It resembles the limestone of Blair, and, 

 like it, is interstratified with talcose, chloritic, and micaceous 

 schists. Some of these schists are carbonaceous, losing 15 per cent, 

 of their weight after ignition*, and present a remarkable wavy bed- 

 ding, with foliated surfaces, and a kind of rude cleavage. The 

 number of different bands of limestone is great in this locality, and 

 their changes of dip and strike endless. AYith a tolerably persistent 

 N.N.E. strike, they overlie the Ben-y-Gloe quartz-rock, and range 

 up Glen Beg, crossing the watershed, and descending again to 

 Braemar. Syenite and porphyry abound, in the form of large amor- 

 phous masses or dykes and veins. 



On the east side of Glen Beg, the beds at the watershed have a 

 marked S.E. dip, which continues also in the quarry about a mile 

 nearer the Spittal. But much careful work is needed in this highly 

 altered region before its geological details can be thoroughly under- 

 stood. Limestone, with a northerly dip, has been quarried two 

 miles south of the Spittal, the intermediate ground being occupied 

 by gnarled schists. 



Much felspathic rock (syenite or porphyry) occurs on both sides of 

 the glen. The strata become very quartzose, in gentle undulations, as 

 we proceed southwards ; and at Lair, a small cottage about two miles 

 from Dalrelzian, they are micaceous flagstones, dipping S.E. at 8°. 



* These schists will be referred to in a subsequent paper, in which we propose 

 to indicate the distinction between foliation and cleavage. The carbonaceous 

 schist was analysed by Mr. Tookey of the School of Mines. 



