544 J. G. H. GODFREY ON THE GEOLOGY OP JArAN. 



This division of rocks is also applicable to the remaining islands 

 of Japan, as according to my experience they are undoubtedly of a 

 geological construction similar to that of Yesso (see Map, p. 543). 

 No proper geological survey of these latter islands has been yet 

 made, and consequently no statement as regards the probable 

 thickness of these groups of rocks can be given. 



1. New alluvium (under which is to be understood the detritus 

 at the present time conveyed from the surface of the hills to the 

 level lands below) is to be found in most places close to the sea- 

 shore, and chiefly in the eastern portion of the main island. The 

 most fertile plains of Japan, as those of Tokei and Kioto, belong to 

 this formation. 



The three mountain-ranges form the centre lines and at the same 

 time also the watersheds of the Japanese islands, and consequently 

 most of the rivers have only a short course and descend rapidly to- 

 wards the coast. Owing to this circumstance and also to the compa- 

 ratively rapid disintegration of the rocks in general, nearly all the 

 rivers in Japan have a tendency to silt up. To prevent inundations, 

 the river-beds are often by artificial means kept at a considerably 

 higher level than the surrounding country. This explains also why 

 Japan, though well provided with running water, is poor as regards 

 rivers navigable for larger vessels than the usual small flat-bottomed 

 craft of the country. 



Sand of magnetic iron-ore, undoubtedly derived from the adjoin- 

 ing volcanic and metamorphic rocks, is frequently met with along 

 the sea-shore and largely used for manufacturing an excellent 

 quality of iron, as, for instance, at Nakayama, province Gueshiu. 



Most of the river-sands, and chiefly those of the northern part of 

 Nippon, contain grains of metallic gold ; but it was only in former 

 times, when wages were considerably lower than at present, that 

 these sands paid for washing. River- sands of a better quality are 

 occasionally worked by farmers in the province of Koshiu during the 

 quiet season. 



2. Old alluvium comprises the deposits of ancient rivers. Usually 

 the various beds are level or nearly so, and are often washed out 

 by the present rivers in their course towards the sea. Sometimes, 

 as in the neighbourhood of Yokohama, terraces are observed near 

 the sea-shore which appear to be due to the repeated raising up of 

 the beach by volcanic action. Careful observations could not detect 

 any proofs of glacial action in the old alluvium ; and consequently it 

 appears to be doubtful if such can be referred to the same age as the 

 drift or diluvium. 



Owing to their formation, the lands belonging in age to the old 

 alluvium are usually situated at a higher level ; but at the same time 

 they are of large extent, and almost equal in fertility to the lower- 

 lying ground of the new alluvium. As regards useful minerals, 

 gold and iron-sand are occasionally met with to a limited extent, 

 and their mode of occurrence is precisely the same as that previously 

 mentioned under the new alluvium. 



3. New Volcanic Bocks. — These rocks, represented by basalt, tra- 



