JIMBu : GEOLOGY OF JAPANE>E SAKHALIN. II 



geolog}' was only guessed at by the nature of pebbles in a river descending from 

 them, and the actual presence of andesite exposures at Ushoro and its environs. 



The volcanic rocks of Sakhalin are mostly pyroxene-andesite. sometimes 

 making a transition into basalt. The andesite often shows columnar and other 

 joints. Some specimens present an old aspect, as at Wäre. Basalt occurs at Otek- 

 koro, Xotasam, the island Kaibato, and other places. Liparite. which occupies in 

 Hokkaido a ver\- extensive area, especially round the mountain-mass of Optateshke, 

 is here almost restricted to the region of Shiraraka. where a reddish-gray compact 

 specimen with a fluidal structure is met with. A white silicified, decomposed 

 liparite occurs at Ruionaibo near the same place. 



The diabasic rock, which turned the coal of the Serutonai coal-field into natural 

 coke, resembles that found in the Chiku-Hö coal-field in Kyushu under the same 

 condition. 



Pretty pebbles of white chalcedony, found near Xa\-oro and other places in the 

 main land, and at many localities in Kaibato. attract the eyes of every tourist, and 

 are derived from the cavities in lavas and agglomerates of usually andesitic nature. 



The vast deposit of pumice, so widely distributed in Hokkaido and also on 

 Kunashiri and other islands belonging to it, has never yet been observed in 

 Sakhalin. 



As regards the distribution of volcanic rocks, we may only state that their 

 principal districts are in the Western Range, not only on its west coast, but also at 

 several places between Xayoro and Manue on the east. On the river Poronai, hills 

 of andesite and agglomerate are found not far below Sakai (formerly probably 

 known by the name " Poronai " after the river itself), that is the place where the 

 2nd. Astronomical Point of the 50th. Parallel is found on this river. On the 

 coast of the Okhotsk sea, similar rocks were observed about 16 km. to the south of 

 Narumi. 



The form of the andesite mountain, along the sea-coast of the region of Poronaipo 

 on Patience ba}', shows its formation as a dyke. 



m. Geological Consideration of Topographical Features of 

 Different Subdivisions of Sakhalin. 



Now we proceed to the characteristics of different parts of Sakhalin, commenc- 

 ing with the ^ledian Depression of fundamental importance. On its northern part 



coast to the north of Pilevo, is of s.'iiiilstone according to Schmidt. The Tusso monntain on 

 the coast of Patience bay is of volcanic rocks, and hxiks conical only in one ilirection. 



