2 Art. 6. — M. Yokoyama : 



The formation which constitutes the plain is divisible into 

 two quite distinct series, the upper which is subaerial, and the 

 lower which is marine. The upper or subaerial series is made up 

 of a brown loam, an altered volcanic ash, wholly devoid of stra- 

 tification and of organic remains, extending in the south as far as 

 beyond Sugita, a sea-side village about 8 kilometres south of 

 Yokohama. The thickness varies according to places, but may 

 attain up to 6 metres. 



The lower or marine series is several hundred metres in 

 thickness. 2) It consists of repeated alternations of different kinds 

 of terrigenous rocks such as clays, sands and gravels which in the 

 lower portion of the series change into shales, sandstones and 

 conglomerates. These rocks are everywhere more or less tufaceous, 

 that is to say, containing materials ejected from volcanoes, but at 

 the same time very rich in organic remains, which are mostly 

 Mollusca, but sometimes plants, worms, echinoderms, mammals, 

 etc. Among the mammals, an elephant called JElephas namadicus 

 Falc. et Caut. first described from the Narbada bed of India 3) is 

 perhaps the most important, 



The strata of this marine series are quite or nearly horizontal 

 in the plain, though inclined and tilted in the peninsula. Brauns, 4) 

 who studied these layers some thirty-nine years ago, believed the 

 presence of a line of unconformability mostly due to the denudation 

 of the layer-surface, not only between the loam and the marine 

 series, but also in the uppermost part of the latter itself. And as 

 he took the shell-layers found just below this lower so-called line 

 of unconformability for Pliocene, he called all the layers lying 

 above it Diluvial, whereby the loam received the name of Upj)cr 



1) The geology of the plain is found in the works of Edmund Naumann (das jetzige 

 Tokio, Peterm. Geogr. Mitteil., 1879, vol. 25) and David Brauns (Geology of the Environs of 

 Tokio, Mem. Sei. Dopartro., Univ. Tokio, No. 4, 1881). 



2) A boring was once driven in Tokyo to depth of over 400 metres without reaching the 

 bottom of the formation (Report of the Earthquake Investigating Committee, No. 45, Tokyo. 

 Japanese) . 



3) Taken by many European authors for Pleistocene, while Osborn of America considers 

 it to be Upper Pliocene (Age of Mammals, p. 355). 



4) Geology of the Environs of Tokio before cited, p. 6. 



