X, A, 3 Smith: Geology of Panay 223 



Mic7'oscopic. — The thin section of this rock is difficult to study 

 owing to the flakes of iron oxide and numerous dark fragments 

 which cannot be easily identified because of their amorphous 

 condition. Fragments of quartz, feldspar, and ferromagnesian 

 minerals are abundant. The whole aspect of the section is that 

 of a clastic rock. Numerous fragments of globigerines and of 

 radiolarian tests are to be seen, but neither the species nor the 

 genera can be distinguished. This rock probably corresponds 

 to the "clay slates" mentioned by Molengraaff" " in his descriptions 

 of certain rocks collected in central Borneo. He gives the fol- 

 lowing description of certain rocks encountered on Poelau Lolong 

 River : 



The country at this point and higher upstream consists of a system of 

 highly folded strata. The strike may be averaged at about E.-W. and E. N. 

 E., but both strike and dip vary considerably. The strata as a rule are 

 highly inclined and not seldom stand vertical. The oldest group in this com- 

 plex is composed of clay-slate, chert, hornstone, sandstone, diabase, diabase- 

 tuff, and diabase-tuff-breccia, also gabbro and serpentine, the latter being 

 derived partly from a variety of olivine-norite * * * partly from picrite 

 or from hartzburgite. * * * gome of the diabases * * * form intru- 

 sive masses, sheets, or dikes in the sedimentary formations and are there- 

 fore younger than these. * * * The cherts are sometimes full of biotite 

 and then resemble silicified micaceous clay-slate, at other times they turn 

 to pure jasper and hornstone. The hornstone is sometimes of a milky 

 white colour, often marbled and alternating with bright red jasper. The 

 chert, and particularly the jasper and pure hornstone, contain Radiolaria 

 and are often almost entirely composed of the tests of these organisms. In 

 the jasper, the Radiolaria can be detected vdth an ordinary pocket lens, and 

 they look like so many round specks, or little grease spots the size of a 

 pin's head. This greasy lustre is caused by the tests of the Radiolaria 

 being filled with an aggregate of quartz which is coarser than the crypto- 

 crystalline composition of the jasper itself. As mentioned before (page 92) 

 these cherts with Radiolaria are of pre-Cretaceous age. 



This also describes fairly accurately what we found on the 

 headwaters of Ulion River. Just what the exact relationships 

 are in this rather confused group of rocks has not yet been 

 determined, but the fact that we have rocks practically identical 

 with those of central Borneo and that they are considered to be 

 older than the Tertiary is very important.'' 



Near the source of Ulion River I found an outcrop of jasper, 

 the position of which was not very clear. In thin sections this 

 proved to be similar to the rock I had described from Ilocos 

 Norte in 1906.' 



° Geolog. Explorations in Central Borneo. Amsterdam (1902), 174. 



" Molengraaff, op. cit., 174. 



' This Journal, Sec. A (1907), 2, 145. 



