20 KOTO : NOTES ON THE GEOLOGY 



firsi lias a facile cleavage but brittle, and consequently becomes 

 lamellar like a brittle micaceous mineral. It is probably identical 

 with the so-called biotite, which we occasionally find mentioned 

 in petrological literature, as being formed from an alteration of 

 olivine, just like as schillerspar has been considered to be a mica, 

 us an alteration-product of enstatite. Recently, Iddings^^ and 

 Lawson-^ described a similar mineral and the latter author 

 named it iddingsite. In the second, we fail to find such a 

 distinct cleavage, and it seems to me to be the same body which 

 Michel-Levy called the mineral rouge''. Now, a question suggests 

 itself to me, whether the red micaceous mineral is identical with 

 the mineral rouge or not ? It is true that the former confines 

 itself to the margin, and in the case where the entire substance of 

 olivine has been transformed to this mineral, the process of 

 alteration has started from the periphery, and it not infrequently 

 happened to me to find every stage of progress from the very 

 beginning to the complete alteration. The latter, on the contrary, 

 starts from the centre in irregular patches, and gradually attacks 

 the whole body but the clear and granulated, thin margin. The 

 formation of the red lamellœ begins with the development of a 

 fine parting which appears like stripes, and which runs parallel 

 to the vertical axis [PL I. Fig. 1) ; while cracks on the margin 

 favour the olivine being changed into the red mineral in the 

 centre. 



In my opinion, there may be a slight diöerence in the 



1) U. S. Geol. Surv., ' ■Münograpli ' XX., p, ;588. Iddings ideiitiiies this iiiincral to 

 tlierniüphyllite, a fi)liated mineral liaving tlic composition of serpentine. 



2) ' The Geology of Carmelo Bay.' Bulletin of the Department of Geology in tlie 

 University of California, Vol. I., p. ol. See also Pirsson's paj^er. Amer. Journ. Sei., XLV, 

 1893, p. 381. 



3) ' La Chaîne des Buys et le Mont Lore,' Bull. Géol. Soc France, 3me Serie, XVIII, 

 1890. 



