31. Verbeek — Geo 7 ogtj of Sumatra. 
443 
complications will ensue when the horizontal pressures are of such a 
direction as to produce a certain amount of lateral shift in the strata 
on either side of the fault, as would be the case in our Illustration, if 
the square of wood were not sawn at right angles to its surface, but 
with the saw on the slant, in which case, the pressures being applied, 
the two pieces of wood would no longer tend to move in the plane 
of the square ; and it is here necessary to remarlc that reversed 
faults resulting from the horizontal pressures accompanying cleavage, 
will not be exhibited on the cleavage faces of bedded slates, except 
where the pressures have a direction similar to that last referred to, 
i.e. such as would produce a certain amount of lateral shift. But 
as this oblique position of the fissures with respect to the pressures 
will be of most frequent ocourrence, we should expect the greater 
number of faults resulting from cleavage pressures to be exhibited 
upon the faces of the slates. 
The above modifications do not, however, destroy the general in- 
ference, that direct faults are indicative of excessive vertical pressure, 
and reversed faults of excessive horizontal, or lateral, pressure. 
IV. — The Geology of Sumatra. 
By M. R. D. M. Verbeek, 
Director of the Geological Survey of the West-Coast, Sumatra. 
(PLATE XIV.) 
(Commuuicated by Professor T. Rupert Jones, F.R.S., of the Royal Military and 
Staff Colleges, Sandhurst.) 
T HE Geological Panorama, Plate XIV., prepared by M. E. D. M. 
Verbeek, is in further illustration of his Memoir 1 “ On the 
Geology of Central Sumatra,” in the Geol. Mag. 1875, New Series, 
Dec. II. Vol. II. (No. 136), pp. 477-486 ; and it gives a view, from 
north to south, of a most interesting part of the Highlands of 
Padang, namely the Oembilien Coal-field. 
To the left the syenite is covered by sandstones and breccias of 
the group “ 5a.” The quartz-porphyry of Mount Toenkar conceals 
the greater part of the Parambahan Coal-field. Then follows the 
Sigaloet Coal-field, with its beds dipping south ; on the other side of 
the Eiver Oembilien the sandstones of the Soengei-Doerian Coal- 
field are seen dipping to the north. These three coal-fields form 
together the Oembilien Coal-field. More to the right (south) follows 
the old limestone with Fusulince , ä and the greenstone (pyroxene- 
porphyry). The hills between the Coal-field and the point from 
•which the panorama was taken are composed of breccias and marl- 
1 See also Geol. Mag. Dec. II. Yol. III. p. 382, for some verbal corrections in 
this memoir; also Vol. II. pp. 532-39, Plates XIII. and XIV., for Mr. Brady’s 
description of some Fossil Foraminifera from Sumatra ; and Geol. Mag. Dec. II. 
Vol. III. pp. 433-40, Plates XV.-XIX., for Dr. A. Günther’s description of some 
Fossil Sumatran Fishes. This coloured Panorama, like the foregoing Plates, has 
been executed under the auspices and at the cost of the Dutch-Netherland 
Government. 
2 In the Neues Jahrb. 1876, p. 41a, M. Verbeek mentions the discovery of 
Productus semireticulatus, rhillipsia, and Goniatites in the Fusulina-limestone of 
Sumatra. 
