GEOLOGICAL OBSERVATIONS IN FIJI. 101 



SEDIMENTARY ROCKS. 



The main types of sedimentriry rocks collected during tlie present 

 expedition were as follows : — 



marl, 



conglomerate, 

 limestone, 

 marble. 



Red sandstones and shales were found in the beds of streams drain- 

 ing the central part of Viti Levu. Their source was not located. 

 Other sandstones, composed of slightly river-worn volcanic materials, 

 were commonly found interbedded with the boulder conglomerates 

 which lie on the slopes of maturely-eroded andesites or form the basal 

 layers of the coastal sediments of Viti Levu. 



Marl. Two types of marl may be found in Fiji. The first type 

 belongs to the folded series of central Viti Levu; the second, forms a 

 part of the coastal -plains series. 



The marl of central Viti Levu is brownish drab in color and has the 

 usual even, fine-grained texture of these rocks. Rocks of this descrip- 

 tion occur to elevations of 2000 to 2500 feet and are often highly 

 folded. 



Under the microscope, the rock shows a paste of limonite, kaolin, 

 and calcite, in which occur many minute, angular bits of quartz and 

 feldspar. Only a few of the feldspars show albite-twinning but their 

 indices of refraction correspond to plagioclase. The twinned varieties 

 have a composition approximating oligoclase or acid andesine. 



The nature of the clastic material found in these rocks would 

 indicate that they were eroded from the granites or diorites of the 

 interior. At the southeastern side of Viti Levu, near Suva, a con- 

 glomerate, underlying flows of andesite and basalt, includes boulders 

 of quartz porphyry and diorite. It is believed the two deposits repre- 

 sent a long period of erosion, in which the plutonic rocks of the center 

 of the island were laid bare. 



The marl from the coastal-plain series bears the popular name, 

 "soapstone." It has a slate-gray color and becomes very smooth 

 and oily when wet. Near Suva, lenses of coralliferous limestone are 

 interbedded with this rock. When dry, the marl has little cohesion 

 and breaks down readily. On exposure the ferrous oxide becomes 



