237 



As the colour makes us alieady suspect, in the tliiii sections under 

 tlie microscope it is to i)c oliservcd, that the rock is chiefly coini»osed 

 of fine dirty-green chloritic particles, which have been altered in 

 the same way as those of the Chamoson-valley '). They contain a 

 fine black dnstlike matter, fiirtlier pretty large grains of ore and 

 moreover a few angnlar splinters of (piartz. Some cavities are tilled 

 with crystals of calcite. 



As to the oolite-formations they distinguish themselves only from 

 the other mass of rock by their structure. In the thin sections tiiey 

 are always of an elliptical or circular shape (diameter 0.08 — 0.6mm.) 

 and consist of very thin green successive coats. The nucleus usually 

 consists of a stranger body, as a rule of quartz, the grain of which 

 occasionally becomes comparatively large (tig. 3). Though its shape 

 may be ever so irregular the coats of tlie chamosite are always 



Fig. 3. 



arranged in such a way that the unevennesses disappear, and the 

 result is in the end a regular oolitic body. There are however 

 likewise fragments of quartz in which every trace of a chamosite- 

 edge is wanting. Exceptionally the fragment of the skeleton of a 

 sponge serves as nucleus of an oolite. In consequence of an altera- 

 tion the oolites change into a yellow- to red-brown mass. 



Formations of chamosite were also met with in other Jurassic 

 sediments of the Kajo-region. As van Nouhuys has already remarked 

 the chamosite-rock changes into another lock of a lighter colour '4n 

 which on the weathering-planes reddish quartz-grains are found". 

 The rock meant here, is a rather course saml.itone, the quartz-grains 

 of which have a diameter of 2 mm. The cement is of a greyish- 

 green colour and effervesces strongly by treatment with hydrochloric 

 acid. In thin sections one consequently perceives nuich calcite, partly 

 in the shape of grains, in which the rhomboedrical cleavage is verj^ 

 obvious, for the greater part however in that of a fine scalish mass 

 forming the real cement. The green chamosite is spread as in the 

 above mentioned rocks, but oolites ai-e only met with as a great 



1) G. Schmidt. Ueber tlie Minei'alien der EiseMOuiillie an der Windgalle im Canton 

 Uri. Zeitschr. f. Krystallogranhie. XI. 1886, p. 598. — Geologisch-petrographische 

 Miltheilungen. Neues Jahib. f. Miner. Beil. Bd. 4. 1886, p. 895. 



