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the eruption of diabases, and to be deposited from circulating solutions 
during or after the eruption. However, there is no reason for attributing 
the formation of the contact-rocks found every where in the Siboumboun 
mountains, to contactmetamorphism by diabases which are not 
exposed; in the northern part we find gabbro, and everywhere 
else granitic rocks . exposed at the very contact. The latter rocks 
are of great extent in the Siboumboun mountains. 
The summit of a small hill on the eastern slope of the Bukit 
Tambang consists of crystalline limestone, in which bands rich in 
garnet and vesuvianite alternate with others containing little or none 
of these minerals. These bands are vertical and rest immediately 
upon a weathered granite, which is crossed by the footpath from 
Timbuloun to Dammer. These contact-limestones are beautiful rocks, 
with excellent contact-mirerals on their weathered surfaces. Also 
siliceous rocks, showing clear signs of contact-meiamorphism in the 
neighbourhood of granites (and gabbro) occur in numerous places in 
the Siboumboun mountains (surroundings of Batu Mendjulor, of 
Limau Purat, of Timbuloun etc); they will not be described more 
closely in this previous paper. Sometimes these rocks much resemble 
those mentioned above, occurring at the contact of granites near 
Pamusian on the left side of the Sinamar. 
The age of the quartz-porphyry of the Siboumboun mountains. 
Quartz-porphyries occur along with the granites, the rocks gradu- 
ating into each other. Probably they are different facies of the 
granites, and of about the same age as these rocks. 
Near the confluence of the river Silaki and its tributary Kapu 
these quartz-porphyries, in immediate contact with the limestone, are 
exposed. Occasionally this limestone, by the development of 
garnet and other contact-minerals, also shows clear signs of contact- 
metamorphism, this fact inducing us to suppose the quartz-porphyry 
also to be of post-carboniferous age. 
It appears from the foregoing that at the contact of various 
granite rocks of the Highlands of Padang a distinct eontactmetamor- 
phism could be stated, and that a carboniferous (or later) age may 
be taken as certain at least for a part of these metamorphosed 
rocks. Thus part of the granites is post-carboniferous of age. 
From the examination of the many rocks which I have collected, 
interesting results may be expected concerning the nature of the 
exomorphic and endomorphic contactphenomena, and the mutual 
connection of the different types of eruptive rocks. 
