JOURNAL OF THE f'OLLEG-E OF SCIENCE. TOKYO IMPERIAL UNIVERSITY. 



VOL. XLIV., ARTTCIiE I. 



Fossils from the Upper Musashino of Kazusa 

 and Shimosa, 



By 



Matajiro YOKOYAMA, Fdfjahuhakmhi, 

 Professor of Palaeontology, Imperial University of Tokyo 



With 17 Plates. 



General Remarks 



The Upper Musashino Formation'^ which consists of horizontal 

 interstratified layers of clays, sands and gravels overlaid only by a 

 brown unstratified loam generally believed to be Pleistocene in age, 

 though without any palaeontological evidence, forms a low but ex- 

 tensive plateau around Tokyo whose height above the sea-level 

 varies from a little over ten metres near the sea-coast up to more 

 than a hundred in the interior. This plateau is variously dissect- 

 ed by valleys along whose sides it often shows steep escarpments 

 fairly well exposing the rock-layers of which it is composed. In 

 these escarpments there is frequently a sand-layer more or less 

 filled with fossils which are mainly Mollusca, and therefore usually 

 known under the name of shell-layer which is found, not onl}^ in 

 and around the city of Tokyo, ^^ but also in Kazusa and Shimosa, 



1) Explained in my paper entitled " Fossils from the Miura Peninsula and its Immedi- 

 ate North " (Art. 6, Vol. XXXIX, Jour. Coll. Sei., Imp. Univ. Tokyo, 1920). 



2) The fossils found in and around Tokyo have already been studied by David Brauns in 

 his " Geology of the Environs of Tokio " (Mem. Sei. Departm. Tokio Daigaku, No. 4, 1885) and 

 S. Tokunaga in his "Fossils from the Environs of Tokyo (Art. 2, Vol. XXI, Jour. Sei. Coll. Imp. 

 Univ. Tokyo, 1906). Brauns described 87 species of Mollusca and Brachiopoda all of which he 

 identified with the living forms and still called them Pliocene. Tokunaga recognized 168 

 species of Mollusca of which he found a little more than 20 not known to him as living (he 

 says that at least 10 ai-e surely extinct). Bat unfortunately he ignored many of the small- 

 sized shells, as difiBcult of determination, whereby the percentage of extinct foruis against the 

 living became not quite correct. Consequently his conclusion, drawn from it, that the layer is 

 probably Pleistocene can not be called quite certain. It is here to be noted that most of the 

 shells described by Brauns and Tokunaga are also found among those described by me in this 

 paper. 



