34 BASIC AND ULTRABASIC IGNEOUS ROCKS— BENSON. 



Gabbros and peridotites are also numerous along a subsidiary tectonic line inserted in the 

 southeastern part of Borneo and the little island of Siboku adjacent thereto, where the serpentine 

 is overlain with Eocene deposits. On the mainland leaving the coast near Cape Selatan, the 

 Meratus range runs to the northeast. Hooze ('93) has traced it for over 50 miles, and his 

 map reproduced in La Face de la Terre (Vol. Ill, p. 337) shows a great series of sheet-like 

 masses of serpentine, gabbro, and diorite invading crystalline schists and older Cretaceous 

 rocks. In the northeast of Borneo the folded Kapua range consists of phyllite but with 

 Mesozoic marls, limestone and radiolarian jaspers associated with diabasic sills and tuffs. 

 There are post Jurassic intrusions of gabbro and serpentine noted here (Molengraaff '02), 

 but the chief masses are on Palawan, where there is a large development of the ultra-basic 

 rocks. When we pass east into the Philippines, the basic rocks appear in several regions from 

 under a covering mantle of generally Tertiary sediments and volcanic rocks. In the incom- 

 pleteness of our knowledge concerning these (see e. g. W. D. Smith '10, '11) nothing is to 

 be gained for our present purpose from a discussion of individual occurrences. We note 

 that the tectonic line, which strikes north into Formosa, is there accompanied by serpentine 

 rocks, while serpentine appears also in the Liu Kiu Islands (Yoshiwara '01). When we pass into 

 Japan the regularity of the serpentine-occurrences is no longer marked, but the information 

 available to the writer does not permit him to give many details. Serpentines and gabbros 

 appear in the basement-complex of crystalline schists. They are again recorded among 'Lower 

 Paleozoic rocks, where they invade a group of more or less metamorphosed tuffs, breccias, con- 

 glomerates, and lavas with intrusive rocks that are pyroxenites, amphibolites, chlorite schist, 

 etc. In the Middle and Upper Paleozoic (Devonian ?) and Carboniferous period there were 

 developed "schalstein" associated with radiolarite, clay, shale, sandstone, and limestone, recall- 

 ing the English and Australian spilitic occurrences, though the eruptions are probably chiefly 

 of Carboniferous age. "Schalstein" and diabase or augite-porphyries intercalated in marine 

 Jurassic rocks are invaded in Shiko-Ku by sills of gabbro and serpentine, and in Eastern Honshu 

 a gabbro grading on either hand into diorite and peridotite is supposed to be of Tertiary age 

 (Inouye '11 and Kozu '13). Thus while there is in this account a suggestion of the possibility 

 of the division of the ultrabasic intrusive masses into the products of Caledonian, Hercynian, 

 and Alpine folding, the two latter being preceded by geosynclinal periods of spilitic eruptions, 

 the evidence as yet is not sufficient to permit a definite statement. 



Apart from these basic rocks in the folded ranges, there is another group of intrusions of 

 a very different character in the foreland-block of Peninsula India. These have been most fully 

 described from the Giridih (Karharbari) coal-field, having been studied by Holland ('95). 

 The rocks described as "mica traps" occur in this and in most of the Bengal (Permian) coal- 

 fields in the form of dikes and intrusive sheets, composed of biotite, olivine, magnetite, chromite, 

 apatite, and a perhaps glassy base. Augite and anthophyllite are present in some instances. 

 The stratified rocks among which they occur are not strongly folded, but form a rather warped 

 faulted basin. The dikes and sheets are younger than some of the faults, but older than the 

 bounding fault of the field. Thus it appears probable that these intrusions occurred during 

 an epoch of crust-faulting and warping, but no marked folding. The rock itself is like the type 

 which is associated with the occurrences of kimberlite-breccia of South Africa and of southern 

 Bavaria, and "forms the peculiar dike rocks which we shall describe from the eastern United 

 States. In petrographic character and the tectonic conditions accompanying their develop- 

 ment these form a definite petrogenetic group, which we have termed the alkaline-peridotites. 



The basement gneissic complex of Peninsula India contains a number of ultrabasic masses, 

 especially in the Madras Presidency (Middlemiss '96 Holland '00), but these give us no evidence 

 of the tectonic conditions that accompanied their intrusion other than that of intense pressure. 

 In Singhbhum, however, to the west of Calcutta, there are three masses of serpentinized perido- 

 tite which are described as laccolitic intrusions several hundred feet thick that have partici- 

 pated in the later stages of the folding of the Dharwar "Huronian" rocks (Fermor, '19). 



