155- The rock is covered at this place by a bed of Rhyolite.
Ser. II. No. 311. River Boelit, near mouth of Banjoe. A light brownish translucent chert occurring as a rounded nodule in sandstone. The chert is crowded with radiolarian casts, principally of Cenosphcera and Cenellipsis. Some of the tests are infilled with chalcedonic silica.
Ser. II. No. 413. From Batang Mahakkam, a district to the east of Central Borneo, as yet totally unexplored. The handspecimen is a brownish translucent chert much cracked by weathering. It is filled with casts of radiolaria.
OuTCROPS of the dlabase-tuffs, MaRLS , and MaRLY Limestones with Radiolaria.
Ser. I. Nos. 554, 558, 559, 560. River Badoengan. The numbers indicate specimens from different beds which on this river overlie each other. They consist of compact, dark, darkgray, greenish-gray, moderately hard, diabase tuff of varying degrees of fineness. They contain usually a small proportion of lime. The radiolaria are, in some specimens, distributed generally through the rock matrix, in others they are limited to the finer grained layers of the tuff, or to small irregular concretionary patches of a browner tint. The radiolaria, for the most part, are only casts, their walls having been dissolved, but not infrequently the walls remain and they are apparently of amorphous or colloid silica. The tests are very frequently filled with a greenish mineral considered by Prof. Molengraaff to resemble viridite; in some instances also by clear silica or, more rarely by calcite. They can sometimes be distinguished by the help of a lens, as minute dark specks in the rock. Sphseroidal and prunoidal forms are common, but less numerous than the Cyrtoidea ; the specimens are distinctly smaller on the whole than those in the cherts and jaspers of the Upper Kapoewas region, and but few species are common to both districts. Mingled with the radiolaria in this diabase tuff there are not infrequently