601 



is slightly sandy -. the residue appears to contain many pyrite- 

 granules and quartz-splinters, while plagioclase, amphibole, pyroxene 

 and andesitic ground mass are decidedly wanting. Between Tji- 

 Keas and Tji Tenreup we find again at the detached hillock Pr. 

 Bondol perfectly analogous clays sloping towards the North at an 

 angle of 14°. A road runs from the Pr. Bondol towards the south, 

 crossing the ridge of the Pr. Maoeng (See map). When I visited 

 this district, the road was under repair, it was even partly torn up, 

 which had required a great deal of digging, so that the disclosures 

 were very interesting. Up to a short distance from the ridge of the 

 Pr. Maoeng the presence could be ascertained of the hard, greyish 

 blue, bulbous shaly clay, getting plastic in a moist condition, 

 yellowish-white when weathering, and constantly declining towards 

 the North. The strike is invariably about N. 70°0, the slope increases 

 from N. to S. from about 15" to beyond 55°. At first we are 

 surprised to see in all brooklets and on the hills immense fragments 

 of andesite, but on closer investigation we discover that they have 

 nothing to do with the rocks of the interior of the hills, as they 

 are the relics of a recent tuff-breccia formation. In one regress of 

 the road we could beautifully observe how a red volcanic area, 

 interspersed with andesitic fragments, overlay discordantly vertically 

 erected, denuded tertiary clay that had been weathered white. 



A geological survey is largely impeded by the circumstance that 

 all over the environs of Buitenzorg suchlike young volcanic agglo- 

 merates overlay the Tertiary, because in many cases the solid stone 

 is found only in deep indentations of the river. Perhaps this is why 

 V and F have indicated so many "miocene breccia" in this 

 district. 



At the watershed of the Pr. Maoeng the regress of the road is 

 10 m. deep; here also are we confronted with the typical blue 

 clay, now, however, declining 28° towards the South. Here we are 

 in the heart of an anticline, in whose northern arm we have 

 encountered a very uniform clay-formation of 1500 — 2000 m. 

 thickness. The clay in the kernel of the anticline also appeared to 

 be next to quartzless and completely devoid of andesitic matter. 



On the Southern slope of the Pr. Maoeng again the Tertiary clay 

 may be noted repeatedly, now sloping down southward. Whereas, 

 however, in the northern arm of the anticline the strike was rather 

 constantly N. TO^'O. it becomes in the Southern arm N. 70° W. to 

 N. 50° W. ; it seems, then, as if the anticline again dips towards 

 the South. South of the confluence of the Tji Djajanti and the 

 Tji Keas disclosures of Tertiary roclcs are over some distance 



