( 149 ) 
It was found on August 26* 1 * 1900 in a boulder bed in the Upper- 
Kajan above the mouth of the kaja*) which is a small rivulet there. 
The dimensions of the boulder (14 X 8 X 8 cM ) indicate transport 
over a not very large distance; probably it was derived from the 
northern slope of the Bawoei Mountains which form the water shed 
between the basins of the Upper-Mahakam and the Upper-Kajan. 
A little further to the East, where NieuwenhCis crossed this range, 
it consists of steeply inclined strata of the old slate formation of the 
Upper-Kapoeas mountains, which are overlaid unconformably by 
horizontal strata of sandstone. 
This leucite rock has the external appearance of a lamprophyr: 
numerous strongly glittering bronze coloured flakes of mica (+3 mm.) 
contrast with a very finely crystalline, but not absolutely compact 
matrix. On careful inspection a very large number of olivine crystals 
may be seen disseminated through the entire rock; only in excep¬ 
tional cases do they reach a size of 2 mm.; they are mostly smaller 
than 0,5 mm. and are noticeable on account of their yellowish brown 
colour and strong lustre. In external appearance the rock resembles 
a minette. 
Under the microscope the matrix is seen to consist of leucite, large 
light green microlites of diopside and numerous small idiomorphic 
crystals of titanic iron ore. The leucite crystals (on the average 
0.05 m.m.) frequently show clearly octagonal and hexagonal outlines, 
others are rounded or have irregular contours; augite microlites in¬ 
cluded in them are arranged more or less concentrically with their 
longer axis parallel to the circumference (fig. 4). At a high magni¬ 
fication and by the use of a selenite disc double refraction and 
twinning laminae can be observed. The diopside-microlites sometimes 
have somewhat larger dimensions and then appear as elongated 
light green pleochroitic prisms without well defined terminal faces; 
they are sometimes twinned. The diopside does not appear as real 
phenocryst. 
The olivine generally forms crystallographically well-defined crystals, 
with well marked cleavage according to (010); the cleavage according 
to (001) only indicated by ill-defined short cracks. The olivine has 
not undergone the slightest alteration, is colourless and transparent 
and generally free from inclusions; the larger crystals only surround 
sometimes a few small crystals of iron ore and augite microlites. 
The mica occurs in two ways, either strongly resorbed — in which 
case the ore grains accumulate in a zone just round the crystal, or 
1 ) A, W. Nieuwenhuis, Quer durch Borneo, II, p. 350. Leiden. 1904, 
