160 Dr. F. M. Stapjf — Sand- grains in Micaceous Gneiss. 



" The reference of the Piora schists to the Carboniferous appears 

 (to Prof. Bonney) to be only a hypothesis " — but, as a fact, I have 

 not made such a reference. I have not dealt with his Piora schists, 

 and would not say anything about them but (Geological Magazine. 

 loc. cit. p. 9) " that they belong to the second of my groujDS (that 

 of the grey garnet schists) and his ' Val Tremola schists ' to the 

 third and fourth group (green, black felspathic mica schists, and 

 amphibolic rocks)." What I have mentioned about the geological 

 age of these (my oion) groups is restricted to the following lines in 

 the Geological Magazine, p. 7 : " If this parallelization be correct, 

 and the metamorphosed sedimentary rocks of the Ursern Yalley 

 properly determined, then we may draw the conclusion that the 

 series of the originally sedimentary rocks on the south side of the 

 St. Gothard begins, at the bottom of the Ticino Valley, with Jurassic 

 deposits and includes Carboniferous at about 1833 m.^ inside the 

 mountain, counted from the mouth of the tunnel." Ibid. p. 10 : 

 " The beds, in which disthene and kindred minerals can be recog- 

 nized at a glance ^ are usually connected with the calc-mica 



schists and black garnet schists, but it would be premature to assert 

 that certain geological horizons in the grey mica schists are charac- 

 terized by the appearance of disthene, etc." Ibid. p. 19: "5 The 

 rocks belonging to the fifth series (on my geological map of the E.R. 

 line), viz. dolomites, grey and green mica schists .... have been 

 characterized in § I.-IIL, where it is pointed out that they extend 

 from the Carboniferous to tlie Jurassic age." 



I have nowhere advanced the hypothesis imputed to me by Prof. 

 Bonney that his Piora schists (my grey mica schists of the St. 

 Gothard Tunnel) belong to the Carboniferous ; and, comparing the 

 Geological Map of the railway line (Explanation on the title-page), 

 the designation Carbon (?) will be found exclusively behind the 

 references for: "Quarzglimmerschiefer mit Chloritglimmerschiefer- 

 lagen. North, PI. Y." ; " Schwarze phyllitische (chloritische) 

 Schiefer mit Kalk — Quarzit — Gneiss-streifen (Oberalpstrasse)." 



On the summary profile (title-page) the designation " Carbon " (?) 

 is restricted to the black schists of the Oberalpstrasse, on the north 

 side ; to the black (and green) schists on the south side, inioards 

 from. 1100 or 1200m. as mentioned above; and to the well-known 

 Manno grits. 



In the bathrologic review (on the same sheet of the map) the 

 schists belonging to V., viz. " Granat-Amphibol-Paragonit-Chlorit- 

 Sericit-Kalk-Glimmerschiefer," are designated as " Archacische ^- 

 Mesolithische Liickenbiisser." 



1 My " grey garnet schists" {sint Prof. Bonney's Piora schists) are reckoned from 

 90-1142 m. ; my "black and green garnet mica schists" from 1142-1833 m. 

 (Geological Magazine, loc. cit. p. 9). 



^ Sint J^Tot. Bonney's " Piora schists." 



^ In the Geological Magazine [loc. cit. p. 19) I have freely confessed that the 

 reference to Archcean was a mistake of mine. 



