594 
PETROLOGY: IDDINGS AND MORLEY 
rocks and at the base of the breccias, and have a wide range of com- 
position. Great sheets of basalt form cHffs with Hmestone west of 
Maros near Patinuan. West of Birau, which is north of B. Saraung, 
there are sills of fine-grained syenite and leucitophyre. Leucitophyres 
form sills in the coal-bearing strata near Batuku. LaccoHthic bodies 
of great size occur at the west base of B. Saraung, also in the valley 
east of Tjamba, and in the valley of Malawa. The rocks forming the 
laccoliths vary somewhat in composition and in grain. The largest 
are shonkinites, fergusite and essexite, which merge at their margins 
into fine-grained and aphanitic porphyries, with small porphyritic 
leucites. Other laccolithic bodies are medium to fine-grained rocks, 
some of which are more feldspathic than the shonkinites, and approach 
monzonites and syenites. There are phases of the laccolithic rocks 
very rich in biotite, augite and olivine, and others, occurring as veins in 
the principal rocks, that are syenites and nephehte-syenites. In con- 
trast to these feldspathic rocks are highly mafic lavas, found as boulders 
in streams, which consist almost wholly of augite and olivine. 
While some parts of the igneous rocks in this region are much de- 
composed, the great majority of the boulders in the streams, and of 
massive exposures in place, are extremely fresh, even the crystals of 
leucite and olivine, although the lavas were probably erupted in late 
Tertiary times. This may be due to the absence of frost and the vigorous 
surface action of abundant rains and strongly flooded streams. 
A large collection of rocks from the localities visited shows the great 
variety of leucitic lavas and the freshness of the rocks in most instances. 
The accompanying chemical analyses of twelve specimens illustrate the 
most interesting varieties so far studied. In addition to the seven anal- 
yses previously published in the Journal of Geology, and those published 
and described by A. Schmidt, they furnish a fair idea of the chemical 
composition of the igneous rocks of this part of Celebes. 
Analysis 1 is of a non-porphyritic trachytic phonohte, which forms 
the summit of Bulu Saraung (Pic de Maros) . It is holocrystalline with 
a trachytoid texture, and consists of prismoid alkalic feldspar with 
abundant minute crystals of what is probably sodalite. There is a 
small amount of brownish green pyroxene, which is shghtly pleochroic, 
colorless wallastonite, and euhedral magnetite. Analysis 2 is of a 
porphyritic pseudoleucite-trachyte, with large phenocrysts of altered 
leucite, now analcite, and fewer of orthoclase and plagioclase. Analysis 
3 is of a porphypitic leucite-trachyte with phenocrysts of augite, biotite 
and altered leucite, in a groundmass of alkalic feldspar and biotite. 
Analysis 4 is of a leucitophyre from Batuku. The phenocrysts of 
