PETROLOGY: IDDINGS AND MORLEY 
593 
in nearly horizontal positions in some parts of the region, but have 
dome-like positions in other places where great bodies of intruded lavas 
have lifted the sedimentary strata and overlying breccias, and have 
formed large laccolith ic masses. The sedimentary strata are also 
traversed by intrusive sheets or sills of igneous rocks which occupy 
sKghtly different horizons in adjacent blocks of faulted sediments, 
showing that their intrusion was subsequent to the faulting and dis- 
location of the sedimentary strata. Dikes of igneous rocks occur more 
abundantly in some localities than in others, but are not very numerous. 
The volcanic breccias, which are probably the oldest eruptions of the 
series in this region, vary somewhat in different localities and in different 
parts of one mountain ridge. For the most part they are basaltic in 
appearance with small phenocrysts of augite and olivine, and very 
few of feldspar. The more feldspathic varieties occur chiefly in the brec- 
cia mountains heading the valley north of Bulu Saraung, that is, 
the southwestern end of the region visited. These rocks are mostly 
trachy-andesites, with small phenocrysts of augite and calcic plagioclase, 
in a groundmass of more alkalic feldspar which is in part orthoclase. 
With these andisitic breccias are associated more basaltic varieties and 
smaller amounts of tr achy tic rocks, some of which contain leucite. 
While most of this breccia is without noticeable bedding, is chaotic, 
parts of it are distinctly bedded and contain well-worn pebbles of the 
same kinds of rock as those forming the chaotic breccia. 
Farther north-east, in the vicinity of Malawa and Batuku, the breccia 
is almost wholly basaltic, with phenocrysts of augite and olivine; 
some varieties containing abundant small leucites, some being rich in 
large leucites. Leucitophyres constitute a great part of the volcanic 
breccias of the ridges visited, and are said to occur throughout a range of 
mountains at least 60 miles in length. Leucite-bearing rocks have been 
found in scattered localities from the Saleier Islands at the southern 
extremity of Celebes to the northern end, a distance of about 500 miles. 
Large bodies of lava have broken through the volcanic breccias in 
places, and have formed masses of trachyte and phonolite. This is the 
case especially in the southwest. The summit of Bulu Saraung (Pic 
de Maros) is phonolite which is younger than the basaltic breccias and 
tuffs that form the ridge to the east. Other large bodies of massive 
lava form peaks north of the road nead Bua. Dikes of porphyritic 
trachyte, and of other kinds of rocks, cut the breccias and sedimentary 
strata beneath them. A large dike of trachyte cuts limestone in the 
valley of the Sangara (Gentungen) above Balotji. It is exposed in a 
wall 6 feet thick and 30 feet high. Intrusive sills occur in the stratified 
