1517 
At a short distance farther up the river, the left wall consists of 
granites. Here groups of sediments occur altered into hornfels, some 
of which appeared microscopically to consist of a quartz-biotite mixture 
with tourmaline, farther up the river light-coloured rocks containing 
garnet and hornfels containing mica being found on the contact 
with the granites, at some meters from the river-side. Downstream 
from the rottan-bridge, very near to it, a complex of strata is exposed, 
the harder rocks of which are stronger weathered out, the softer 
layers being washed away. The hard rocks probably are partly 
silicified marly rocks, crystalline to a small degree or not at all, 
sometimes showing light-coloured circular or elliptie sections that 
look much like those of the erinoid-roeks and -marls of Timor. I 
am strongly inclined to suppose the metamorphosed rocks of the 
contact above the kampong of Pamusian not to be older than carboni- 
ferous. Similar contactmetamorphie rocks are of large extent in 
the Siboumboun mountains and there too they may easily be explained 
by contact-action of the granites. 
Down the river from the kampong, at the first turn of the river 
to the right, rocks of granite emerge from the water when the level 
is not too high, on the left bank coarse-crystalline white limestones 
being exposed near the granites; macroscopically no contact-mine- 
rals could be observed in these limestones. At a short distance 
farther up the river on the left side, weathered granitic rocks with 
hard unweathered nodules are exposed, this being a characteristic 
often shown by these rocks also elsewhere in the Highlands of 
Padang. 
B. Right side of the Sinamar. Near the rottan-bridge on the right 
bank granite is exposed in a steep wall. Farther down the river, the 
right bank lies thickly strewn with huge blocks of dark fine-crystal- 
line hornfels, in some blocks the very contact with the granite being 
visible, whereas in others irregular granite-apophyses occur. Here too 
granite and its contact rocks are accidentally exposed as solid 
rocks. 
This fine-erystalline dark hornfels macroscopically much resembles 
the felspar-hornfels described by the author at the contact of the 
granitic area of the Rokan-regions'). VErBerk*) already mentions 
felspar hornfels of Pamusian; he describes them as dark-grey, fine- 
crystalline very hard rocks, which macroscopically appear to consist 
1) H. A. Brouwer. On the granitic area of Rokan (Middle-Sumatra) and on con- 
tact-phenomena in the surrounding schists. These Proc. XVII (1915), p. 1190. 
2) R. D. M. Vergeex. 1 c. p. 179. 
