2

348

It appeared immediately that the above-mentioned specimen hasnothing to do with clay-slate, but is a genuine eruptive-rock showingexcellent pipemo-stmctuve. The dark brownish-red faint colour of thechief mass seems to have given rise to Evkkwijn’s error. Characteristicare the numerous lens- or disk-shaped “Sehlieren” ending in a point,which, being arranged more or less parallel, contrast sharply withthe groundmass. The specimen is distinguished from the typicalpiperno by the much more intimate connection between “Sehlieren”and groundmass, and by its inferior porosity.

The analysis of the rock (I), for which I am indebted to Prof.I)r. M. Ditthicii of Heidelberg gave the following result:

I

11

Si 0* .

. . 67,37.

. . 69,04 -

Ti ()’ .

. . 0,69.

. . -

APO 3 .

. . J 2,53.

' ' J 17,09

Fe’ 0*.

. . 6,37.

FeO .

. . 0,49.

M n ().

. . trace .

Cat) .

. . trace .

. . 0,74

MgO .

. . 0,97.

KM) .

. . 10,01.

. . 9,74

Na*0.

. . 0,03.

. . 2,34

CO 2 .

. . trace .

. . -

j under 110°| over 110°

' oss °f iiicandesc. 0,94

. . 1,36

100,38

99,89

From this analysis it appears that among all the

rocks that have

itherto been found in the

Indian Archipelago, the

above-mentioned

eruptive rock is richest in potash. From the — alas incomplete —analysis II communicated at the same time 1 ) appears further its

Pelapis Tiang Balei granite and in the N.W. part clay-rocks

Pelapis Genting „ „ „ „ N. ,, „

Pelapis Rambai „ ,, „ „ N.E. „ ,,

Pelapis Tekik (Pelapis Tukang Kluwar) „ ,, „ „ N.W. half „

Pelapis Suka ,,

Pulu Dua and Pulu Bulak clay-rocks.

This does not imply, of course, that all that was called by Everwijn clay-slate,sli old be classed with the rhyolitic rocks.

i) Carl von Hauer. Rhyolith aus dem Eisenbacher Thai. Verbandl. k. k. gcolog.Reiclisanst. Wien. 1868, p. 386. *