82 THE GEOLOGICAL STEUCTTJEE OF SOUTH COENWALL. 



I also sent a pieco of the rock to Professor Jucld of the Eoyal 

 School of Mines, requesting him to favour me with his opinion 

 thereon. The following is the Analysis : — 



per cent. 



Moisture 0-00 



Combined Water 0-90 



SiHca 76-85* 



Alumina 15"05 



Ferric Oxide 0-50 



Ferrous Oxide .. .. 1-80 



Lime 0-10 



Magnesia 0*10 



Potash 1-39 



Soda 2-33 



Loss 0-98 



100-00 



Specific gravity 2-587 



* Of this 1-05 per cent, soluble in acid. 



Professor Judd's reply came to me through my son, and is 

 to the following effect — " That of all the rocks with which he is 

 acquainted it resembles most closely in characters, structure, and 

 composition, the well-known rock of the Schuttrisberg near 

 Schemnitz, a rock which has been pretty generally described by 

 petrographers as a " gneiss." He would call it almost indiffer- 

 ently a " mica-granulyte " or a fine-grained red gneiss." In 

 another letter I learn that the Professor had found minute 

 garnets in the specimen I had sent him. I too had seen garnets 

 in the rock in some of the specimens (a very common accessory 

 mineral in gneiss rocks), but had omitted to mention the fact to 

 the Professor. I cannot think it necessary to say more on this 

 point. 



3. — The Age of the Fowey Beds. — Mr. Somervail condemns 

 my suggesting that these may be Upper Silurian. He states that 

 they are "charged with typical* forms belonging both to the 

 Lower and Middle Devonian," and says further "I am not 

 aware that any geologist of the present day besides Mr. Collins 

 himself has attempted to identify them with the Upper Silmian." 



* On my sketch map these beds are marked as Upper Silurian with a 

 query (?), They were so marked originally in the text also, but the query (P) has 

 been omitted by an error of the press, which I did not observe in time to correct. 



