102 



GEOLOGICAL RESEARCHES IN 



ments of a green serpentinoidal rock, which seemed to be a variety of the 



amygdaloid, occur in the creek. 



September 4th. Descending to the sea we rode southward along the shore, 



under cliffs of the volcanic conglomerate, as far as the large village of Kumaishi. 

 September 5th. Leaving Kumaishi we followed the beach southward. From 



the village south the shore bluff is formed by a vertical cliff of white pumice-tufa, 



sufficiently hard to permit the making of steps in it. It is in thick beds having 



a southerly dip. South of Hiratanai this pumice-tufa is covered by the usual 



tufa-conglomerate. 



A short distance east of Hiratanai a flow of amorphous lava, resembling that 



which occurs in fragments in the conglomerate of Isoya and Futoro, flows over the 



face of the bluff — the erosion of the 

 conglomerate having progressed to 

 nearly its present condition before 

 the flow. A conical hill with a 

 crateriform depression, lying several 

 miles inland, was observed from the 

 beach, and was possibly the source 

 of the stream. 



Beyond this point, as far as To- 

 marigawa, another bed of pumice- 

 tufa, overlying the conglomerate, 

 terraces that extend several miles 



a. Lava flow. b. Tufa-conglomerate. 



forms the bluff-rock and the skeleton of the 

 inland. 



At Tomarigawa we left the sea-shore and entered the mountains, and ascending 

 to the watershed between the Japan sea and Volcano bay, we descended the eastern 

 slope to the mines of Yurup. 



Our road, during this distance, lay, all the way, over the volcanic tufa-conglomer- 

 ate formation, which extends entirely across this part of the island, and forms the 

 ridge at a height of perhaps 2,000 feet. 



This deposit is cut up by deep valleys with steep sides. In these I noticed out- 

 crops, beneath the conglomerate, of granite, two or three miles from the sea, and, 

 further eastward, of the argillaceous rock with vermiform fossils already mentioned 

 several times. 



The lead mines of Yurup are in the valley system of the river of the same name. 

 Here a widely extended erosion has removed the volcanic congk)merate, for a 

 considerable distance, exposing a very extensive development of a black meta- 

 morphosed argillite, which was found to contain the vermiform fossils so often 

 mentioned in the previous pages. The strata are tilted up, often almost vertical, 

 and are frequently connected with broad bands, apparently dykes, of greenstone. 

 The lead-bearing veins occur in both these rocks. The vein-mass consists of quartz, 

 carbonate of manganese, calcite, and, in one vein, crystals of barytes. Besides 

 these minerals the galena is associated with zincblende, and pyrites of iron and 

 copper. 



The veins vary from two to eighteen inches in thickness, being more regular in 



