276 BE. J. W. GREGORY ON THE WALDENSIAN [May 1 894, 



Fig. 4. Part of the thickest aplite-dyke from the same locality. It consists, in 

 the main, of quartz-orthoclase mosaic and bands of mnscovite; it 

 contains included grains of the surrounding rucks, like that seen in 

 fig. 3. 



42 



Figs. 5 & 6. The Contact-series at Ostana, near Crissolo, Po Valley. X 77- 



Fig. 5. The contact-rock; all the minerals are authigenous or due to injection 



from the gneiss ; the rock consists of orthoclase (0), quartz-orthoclase 



mosaic, biotite (b), and zoisite aggregates (3). 

 Fig. 6(a). The lead -coloured mica-schists, 100 yards from the contact. 

 Fig. 6(b). The gneissose mica- schist near the contact; the principal secondary 



minerals produced are garnets (gr), often traversed by veins of 



chlorite, muscovite (m), and rutile (m). 



All the figures are drawn under ordinary transmitted light. 

 DlSCTTSSTOK. 



The President felt sure that all would join in offering a welcome 

 to Dr. Gregory on his first appearance at the Society, as an Author, 

 since his adventurous African journey ; and he further expressed a 

 hope that, ere long, the Society would hear something, of the 

 geological features of Mount Kenya. 



The paper contained some startling conclusions in respect to the 

 lowest rocks not necessarily being the oldest ; but for these we had 

 been more or less prepared by the work of Lawson in America and 

 of Barrow in Scotland. Hence there was no a priori improbability. 

 The question was whether the evidence and arguments in this case 

 favoured the notion of a gneiss having been intruded into schists. 

 He (the President) thought it was so, though without further proofs 

 as to age it might be merely an instance of an Archaean gneiss 

 intruded into Archaean schists. Thus it became important to 

 determine, if possible, the age of the schists. He commented on 

 the fact that no fauna lower than the Carboniferous had been dis- 

 covered in the Western Alps, and expressed curiosity to know what 

 had become of the older Palaeozoics : the discovery of radiolaria 

 may possibly lead to results of importance in this direction. 



But by far the most astonishing part of l)r. Gregory's paper is 

 the last, where he speculates on the age of the gneiss itself, and 

 concludes that, owing to its freedom from the effects of earth- 

 movements, it is actually amongst the youngest rocks in the 

 Alps. On this point, more especially, he expected an animated 

 discussion. 



Prof. Jujdd said that all his prepossessions were in favour of 

 accepting the views of Dr. Gregory concerning the hypogene origin 

 of these gneisses and their late geological age. He felt, however, 

 that, in a district which has undergone such great movements, the 

 evidence brought forward must be scrutinized with the most ex- 

 treme care. He was not satisfied that the evidence of contact- 

 metamorphism, of included fragments, and of apophyses of aplite 

 proceeding from the gneiss into the schists had been established 

 beyond every possibility of doubt. 



