172 RevieiDs — Dr. Molengraaff's Central Borneo. 



There are three principal volcanio areas in Central Borneo, the 

 Miiiler mountains, the northern slope of the Schvvaner mountains, 

 a,nd on the Samba river. The most important is the Muller range, 

 forming the south boundary of the Upper Kapoewas plain ; its 

 known extent in an east and west direction is 280 kilometres, and 

 its average breadth about 45 kilometres. The whole of the range 

 consists of volcanic rocks ; those of the western portion are of 

 a decidedly andesitic character, and those of the eastern of rhyolitic 

 and dacite types. Thick beds of tuff are also present in which there 

 are large quantities of silicified wood, partly stems of trees still in 

 an upright position. The average height of the mountain peaks, 

 vsrhich are mere fragments of a former unbroken tuff- plateau, is 

 about 1,100 metres. The volcanic action which produced these 

 mountains is believed to have commenced during or shortly after 

 the Cretaceous age, and, after continuing through the Tertiary, 

 terminated probably about the commencement of the Quaternary 

 period. 



In an appendix. Dr. G. J. Hinde gives a description of the 

 Radiolaria which form a large part of the chert, hornstone, and 

 jasper series of rocks, and are present also in the alternating beds 

 of diabase-tuffs, marls, etc., belonging to the Danau formation, 

 mentioned above. The unexpected discovery of these siliceous 

 organic rocks in Central Borneo by Dr. Molengraaff is of considerable 

 interest in view of the fact that within the last few years rocks 

 of a similar character have been found in other parts of the East 

 Indian Archipelago, at Celebes and Billiton, and also in various 

 parts of Europe, in California, Australia, and Japan. 



About one hundred different forms of Eadiolaria were recognized 

 and described in thin sections of these Central Borneo rocks, and 

 figures of them, carefully drawn by Mr. A. T. Hollick, are given 

 on the accompanying Plates. Of these forms, seventeen occur in 

 the rocks of other countries, and eighty-three are at present only 

 known to Borneo. They show many points of resemblance to the 

 Radiolaria present in rocks of Jurassic age in Switzerland and Italy, 

 and to those of approximately the same age in the coast ranges of 

 California, and it is highly probable that the deposits in Central 

 Borneo in which they occur are likewise of Jurassic age. 



In concluding our notice of this most interesting and valuable 

 work, we wish particularly to call attention to the series of maps, 

 oharts, and sections in the atlas, and to the striking photographs, 

 illustrating the natural scenery and geological structure of the 

 country, and giving lively i-eproductions of the people, their homes, 

 both for the living and the dead, and the strangely carved figures 

 and memorial poles which surround their settlements. In the 

 charts of the rivers the salient geographical and geological features 

 of every portion of their course are carefully noted, and the geo- 

 logically coloured maps and sections enable the reader readily to 

 follow the observations recorded in the text. 



The author acknowledges his obligations to Messrs. Schlumberger 

 and R. Bullen Newton for determining the Nummulites ; to Dr. Krause 



