KELATION TO MESOZOIC ROCKS IN THE LEPOJsTINE ALPS. 2:^7 



Pass, but here of only about '02 inch or -03 inch in length, together 

 with a pale green hornblende, brown mica, and some quartz. This, 

 schist is much crumpled, evidently by the action of pressure 

 subsequent to mineralization. 



In this connexion it may be well to notice the rock in the Yal 

 Canaria mapped by Von Fritsch as " Disthen-schiefer," and fully 

 described by Grub'enmann, although the distinctive mineral is far 

 less conspicuous than in the cases already mentioned, and in one 

 instance he failed to find it. He describes this schist as " zweiglim- 

 merigen {sog. Disthen fiUirenden) Schiefer ; " and undoubtedly micas 

 are the more conspicuous minerals. Its position in the supposed 

 fold of the Val Canaria has already been described, and just above 

 the upper mass of rauchwacke is a schist which, macroscopically, is 

 identical, and only differs under the microscope hj the absence of 

 the disthene *. Dr. Grubenmann states that the rock also occurs 

 in the ravine leading up from the Lake Ritom to the pass between 

 Pian Alto and Fongio, and in this view I entirely concur. For a 

 full description of the microscopic structure, I must refer to his 

 paper ; but it will suffice to say that the rock in the lower zone 

 (where it is altogether about 6 feet thick) is of a grej^-green to dark 

 green colour, with a pearly lustre on the cleavage-surfaces, and 

 occasional marked folia of a dark mica. Among these occur in- 

 folding layers of mica with a wavy cleavage, and with these are asso- 

 ciated small blades of disthene, with quartz and calcite. Two micas 

 are present, one colourless the other dichroic ; they are associated 

 with needles of rutile. Tourmaline occurs pretty frequently, with 

 some zoisite, black grains of iron-oxide (doubtless magnetite), 

 pyrite, and zircon. From a discussion of the optical properties of 

 the micas, and their analyses (given below t), Dr. Grubenmann 

 considers the colourless one to be a kind of margarite, and the 

 dark one a meroxene. They occur roughly in the proportion of 

 20 : 9. 



* As I follow Dr. Grubenmann in the description of the rock, I will retain 

 in this part of my paper the name disthene instead of kyanite, which I am in 

 the habit of using for this mineral. In my specimen, however, there are some 

 emall-bladed lamellse which, I think, may be identified with disthene, and 

 several rather irregularly formed granules of a honey-yellow mineral, wliich 

 much resembles staurolite. These are about "01 inch long. 



t 



SiO 



The White Mica. 

 I. 

 34-90 



II. 



34-82 



48-85 



trace 



10-83 



2-69 



0-59 



3-30 



The Dark Mica. 

 I. 

 SiO, 40-5B 



II. 



40-96 



Al.,03 

 Fe"0, 



48-92 



TiO; 0-38 



Al^Og 21-84 



0-43 

 •>2-10 



trace 



10-88 



2-33 



Cab.l 

 Na,0 



Fe^Oy 6-02 



FeO 5-91 



MgO 1408 



K.,0 ()-41 



Na.,0 3-07 



H2O 2-31 



7-25 



5-27 



1413 



5-87 

 3-19 

 2-25 



K 



0-49 



H2O.. 



3-05 





100-57 

 gr. =3-1095. 





101-08 



Sp. 



100-58 

 Sp.gr. 2-9001. 



101-45 



