732 
and of grey very sandy coral marls containing even sometimes 
gravel, towards the top they gradually change into the clays, sands 
and gravels, which constitute to the West of the river Sekurau the 
youngest part of the tertiary formation. Whereas the group of 
the calcareous rocks in the miopliocene westward of the river 
Sekurau has only a thickness of a few hundred meters — and still 
farther in a western direction quickly diminishes in thickness — it 
has become in the Sungei Narut, towards the Sekerat Mountains, 
1000 m. thick or more. Traces of dead black coal between the 
coral sands and marls in the Sg. Narut and of transitions between 
glance coal (anthracite) and dead black coal in the deepest denudation 
of coral marls in the Sg. Mampang indicate that we have here to do 
with a modification of facies at a short distance, that the “younger 
coalbearing tertiary formation with limebanks” to the west of the 
river Sekurau is replaced by a system of sandy marls and coral 
limestones. constituting a great part of the Sekerat Mountains. 
A transition of facies of much inferior interest in the old-miocene 
containing glance coal (anthracite) takes place in the neighbourhood 
of the Sekurau anticline. Whereas in this formation coal strata are 
still numerous in the southern part of the Sekurau anticlinal, their 
number rapidly diminishes, so that the older miocene in the Northern 
part of the Sekuran antielinal, on the Sembulu anticlinal and on the 
South and North Sampajau anticlinal is very poor in coal seams. The 
consequence of this modification of facies is, that in these regions 
we can no longer separate the “oldest coal-free posteocene” and the 
“old miocene containing glance coal” (anthracite) from each other 
in a satisfactory manner. 
In the centre of the domeshaped Sembulu anticlinal, which is 
less strongly folded than the Sekurau anticlinal, we find hard shales 
and sandstones, belonging certainly to the old-miocene containing 
glance coal (anthracite), though the coal is entirely wanting, — with 
the exception of a few unimportant seams only some centimeters 
thick and numerous traces of coal on the planes of the strata of the 
sandstones. On the Northwestern limb limestones with small Lepido- 
eyelinae occur besides the typical sandstones and argillaceous shales. 
On the South-eastern limb we find — still in the old-miocene and 
alternating with the hard shales — exceedingly fine strata of usually 
grey clayey sands and sandy clays which often contain shales. In 
the Northern part of the Eastern wing these clayey sands change 
towards the top gradually into a thick system of Globigerina marls, 
sandy and even gravel-containing limestones and grey, clayey sandy 
marls rich in fossils of a littoral origin. The Globigerina marls are. 
