ABSTRACT
In the greater part of the sedimentary deposits met with in Central Borneo no fossils have hitherto been found, so that an absolute determination of their age is in most cases impossible, and even a relative determination is generally doubtful. As a matter of fact in West Borneo, to the east of Sintang, there exists only one system of strata the age of which is known. This chapter presents a summary of the formations and rocks which take part in the structure of that portion of Central Borneo which has been investigated, must therefore of necessity be provisional and to a certain extent uncertain. The age of the old slate-formation is unknown, but that there are reasons for supposing that it is probably older than the other sedimentary formations hitherto known in Central Borneo. The existence of deposits of Eogene age in Central Borneo has been identified in boulders of a grit, resembling greywacke with Nummulites and Orbitoides.
