1516 
some of which orthoelase occurs with plagioclase and quartz, may 
be in genetical connection with granites. 
Although the limestones will provisorily be regarded as of car- 
boniferous age, we must point to the fact that Vorz*) has found in 
limestones of this area a Milloporide, Myriopora Verbeeki, which 
corresponds to the Stromatopora Japonica which has already been de- 
scribed by YaBw®), and has been found in intermediate strata between 
the jurassic and eretaceous formations in Japan; thus various lime- 
stones of Sumatra, the age of which had hitherto not been deter- 
mined, may be much younger (late mesozoic). 
The constitution of the rock between Ahour and Tampouroungo, 
described by VerBEEK as a quartz-diorite, also contains far more 
plagioclase than orthoclase ; although elsewhere occur some veins of 
quartz-dioritein granitite, still often the two roeks graduate insensibly 
into one another, which points to about equal age. In connection 
with a small seam of a malacolite rock occurring near Ahour at 
the contact of the quartz-diorite with carboniferous limestone, VERBEEK 
considers it possible that this quartz-diorite is post-carboniferous. 
Contact near Pamusian. 
The kampong of Pamusian on the Sinamar can be reached by 
various footpaths from the road Pajakombo— Bua, e. g. from Halaban. 
One passes the Sinamar over a very primitive swinging bridge of 
rottan. Near this bridge, down the river, contacts of granite with 
various metamorphic sediments are exposed on both sides of the river. 
A. Left side of the Sinamar. Between the kampong and the 
bridge of rottan, when the water-level is not too high, the contact 
of granites is plainly uncovered on this side of the river. Up the 
river from the kampong, we find at the contact a complex of often 
banded, compact to  fine-crystalline siliceous rocks, among which 
occurs dark-coloured fine-erystalline hornfels containing much biotite. 
The macroscopically compact rocks also show clear signs of con- 
tactmetamorphism ; from a preliminary examination of some samples 
on 7 or 8 metres from the contact, light-coloured parts turned 
out to consist of a mixture of quartz with grains and short erystals 
of augite, or of a mixture of quartz and feebly-coloured amphibole 
with or without flakes of brown biotite. Occasionally also calcite 
occurs in these rocks. In the darker coloured parts the biotite can 
sometimes be seen with the naked eye. 
1) W.. Vorz, le. p. 755. 
9 
2) H. Yase, On a mesozoic Stromatopora, Journ. Geol. Soc. Tokyo 1903. 
