374 CELEBES. [chap. xvi. 



The geological structure of this part of Celebes is 

 interesting. The limestone mountains, though of great 

 extent, seem to he entirely superficial, resting on a basis 

 of basalt which in some places forms low rounded hills 

 between the more precipitous mountains. In the rocky beds 

 of the streams basalt is almost always found, and it is a 

 step in this rock which forms the cascade already described. 

 From it the limestone precipices rise abruptly ; and in as- 

 cending the little stairway along the side of the fall, you 

 step two or three times from the one rock on to the other, 

 — the limestone dry and rough, being worn by the water 

 and rains into sharp ridges and honeycombed holes, — -the 

 basalt moist, even, and worn smooth and slippery by the 

 passage of bare-footed pedestrians. The solubility of the 

 limestone by rain-water is well seen in the little blocks 

 and peaks which rise thickly through the soil of the 

 alluvial plains as you approach the mountains. They are 

 all skittle-shaped, larger in the middle than at the base, 

 the greatest diameter occurring at the height to which the 

 country is flooded in the wet season, and thence decreasing 

 regularly to the ground. Many of them overhang consider- 

 ably, and some of the slenderer pillars appear to stand upon 

 a point. When the rock is less solid it becomes curiously 

 honeycombed by the rains of successive winters, and I 

 noticed some masses reduced to a complete network of 

 stone, through which light could be seen in every direction. 



