G.A.F. Molengraaff 
Geological Explorations in Central Borneo (1893-94) [PDF ebook] 

This book, first published in 1902, is the product of the detailed geological survey undertaken by the Borneo Expedition of the late nineteenth century. The scientific exploration focused on Central Borneo, especially the sources of the Kapoewas and its tributaries, and its analysis of the geology of the region still today forms the bedrock of research into the area.