The Nanggulan Formation is one of the oldest rock formation in Mountain of
Kulonprogo. It litologically consists of sandstone with inserted lignit, sandy marl,
claystone with limonit concresion, limestone and tuff rich in foram fossil. To study the
foram fossil contained in this formation, identification process should be done by
taking rock samples on Line Kalisonggo, Kalisonggo Hamlet, Village Pendoworejo,
Girimulyo, Kulon Progo, Yogyakarta. The study begins with a field survey to
determine point of sampling research. Rock samples were taken from 12 points of
sampling research. Foram fossils obtained by wet sieve method. This method can be
described as follows: each sample of rock was pulverized, after that inserted into the
bottle and then added by water detergent sufficiently. The bottle is shaken out and
replaced the water until the grain of rock was visible. The grain was filtered using a
micro filter stratified (by 4 levels) with a sieve size of 0.99