﻿M. Verheek — GeoJogij 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 rigid 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 remark 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 occurrence, 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, howevei*, 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 op Sumatra. 



By M. E. D. M. Verbeek, 



Director of the Geological Survey of the "West-Coast, Sumatra. 



(PLATE XIV.) 



(Communicated by Professor T. Rupert Jones, P.R.S., of the Eoyal Military and 

 Stail Colleges, Sandhurst.) 



THE Geological Panorama, Plate XIV., prepared by M. E. D. M. 

 Verbeek, is in further illustration of his Memoir ^ " 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 " oa," 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. ThesS three coal-fields form 

 together the Oembilien Coal-field. More to the right (south) follows 

 the old limestone with Fusidince,^ 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- 



^ See also Geol. Mag. Dec. II. Vol. 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. Giinther'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. 415, M. Verbeek mentions the discovery of 

 Productus semireticulatus, FMUipsia, and Goniatites in the Fusulina-limestone of 

 Sumatra. 



