Correspondence — Prof. P. Martin Duncan. 239 



rocks, but apatite is always found ia them, while tridyinite occurs 

 not unfrequently. 



The author described a number of structural variations in the 

 augite-andesite from different localities. Among the most interesting 

 is a variety containing as much as 69 per cent, of silica. 



Among the less abundant rocks are the enstatite-andesite, the 

 quartz-augite-andesite, and the hornblende-andesites. The plagio- 

 clase-basalts of Japan can only be distinguished from the augite- 

 andesites by the presence in them of olivine. Magma-basalts are 

 rare, most of the varieties being of the dolerite type ; but under the 

 name of " basalt-lavas " the author describes varieties with a glassy 

 base. 



In an Appendix some account is given of a number of pre-Tertiary 

 rocks, including; grranite, one varietv of which contains the new 

 mineral, reinite, of Fritsch (the tetragonal form of the ferrous- 

 tungstate), quartz-mica-diorite, diorite-porphyry, and diabase. 



COS/iE-DSSiFOlsriDIBn^GJZ]. 



EEPLT TO PEOFESSOR LINDSTEOM. 



Sir, — T am much obliged to Prof. Lindstrom for giving a correct 

 translation of the generic diagnosis of Pholidopliyllum. He has 

 possibly a right to complain that in my communication to the 

 Geological Society the word lilcformigld was translated lUce-formed, 

 but I am free to confess that I do not understand the term which he 

 uses, " homogeneous stereoplasma." With regard to the unfortunate 

 mistakes in the spelling of generic names, I find, thanks to Mr. 

 Dallas, that my manuscript is still in existence, and that I was 

 correct. My reliance on the able reader of the printers of the 

 Society was unfortunately in this instance impossible, for he was 

 taken from amongst us. Hence the errors in print. 



Prof. Lindstrom, when he comes over to England, will find at 

 the Museum in Jermyn Street, and at the British Museum, specimens 

 of what he calls Pliolidophjlkmi from the Upper Silurian of England. 

 On the other hand, he will find specimens of all the species of 

 Falaocydus, Ed. and H., without a trace of the characteristic 

 exothecal (or whatever they may be) structures of PJwlidophyllmn. 

 In many the outside is so well pi'eserved that there is no trace of 

 the structures any more than there is to the eye in the lithograph, 

 fig. 20, plate viii. of Prof. Lindstrom's work on the Operkelbarande 

 Koraller, Stockholm, 18S2. I have looked into the subject with 

 some care, and I still believe that his curiously covered corals are 

 not of the same genera as those described by Edwards and Haime. 

 Those authors do not mention these structures, which would have 

 been palpable enough to their sight if they had existed in their 

 forms. 



But there is another way of looking at the question, which inter- 

 feres with the value of Pholidojjhylhim as a genus. What is the true 



