CHAPTEE YUl. 



SUMMARY. 



It would Ijc perfectly cleiir, I believe, even without the assistance of the 

 facts Cdntaiued in the l'oiei;;oiiiij; chapter, that the shell-la)'er.s which are the; 

 suhject of the 4th, 5th, and (Jth chapter, tliongli they are very young, yet belong 

 to the tertiary formation. For the Tolcio-and Yokohama-exposures exhibit an 

 vnconformahiliUj which separates the bulk of the diluvial formation (divided in 

 itself by another line of nnconfonnability) from an underlying formation, and 

 the latter contains a molluscous fauna com[)rising living species, many of 

 which arc not r,ow foiuid in the neighhoiu'liood of Ja'pan nor even in the Pacific. 

 Besides, in some localities within the Tokio plain, the strata below tlie same line 

 of unconformability liave a di]i of 5 to 6 degrees, wliilst the diluvial strata are 

 horizontal. 



To illustrate~tlie character of the fauna, I resume that in the upper tertiary 

 deposits of the environs of Tokio and Yokohama 87 species have been determined. 

 Two of them, I)ent<alinm octogonum Lamarck and D. cntale L., belong to the 

 Solenoconchaj; one of Ihcm is recent and Japanese, the other exclusively found 

 in the Atlantic. A third species belongs to the Brachiopoda and is recent and 

 Japanese. The rest are 41 Gasteropoda and 43 Conchifera. Among the for- 

 mer, 9 are neitlier Japanese nor Chinese; if we include the sjiecies described by 

 Gould from Hongkong or its vicinity, e. g. Cerithiopsis rugosa, Monoptygma 

 puncticulata, the two Odostomiao, as indigenous in the neighbouring seas, the 

 number of the indigcnoTis species is ö2. The rest includes only oueboreal univabe of 

 the Pacific Ocean, Trichotropis coronata Gld, not found hitherto further south 

 than the strait of Semiavine. Tiic remaining species are Atlantic, and though 

 none of them are really extinct, they are geographically sejiarated by a wide 

 interv.-d from the living Japanese fauna. I\Iost of (hem are very often found in 

 u fossil state, just as a certain nundjer of the oiher 32 gasteropoda, especially 

 those which at present are common to the Atl:intic and I'acific Ocean, e. g. 

 Colnmbclla scVipta L., I'urpnra lai)ilhis Ij., C'himnitzia elegantissima Mont. — 

 Among the 4.3 Oonchifi^'a (here are only 7 which are not living in the Ja]i,'inese 

 sea, and among (hem wo find 2 boreal Pacific s])ecies, Panojmea generosa (Jould 

 and Lyonsia flabellata Goidd, the former going southward to Oregon liu( mil to (he 

 East-Asiatic temperate coasts. But (he other T) are important species, viz. Kellia 

 Ruborbictilaris Mont., Luciu.a boreal is L., lliplodonta trigonula I'e: h , Yoldiaarcdca 

 L., an important arctic fonn, and abos'c all Limopsis aurila Brocchi, which belongs 

 to a genus wliose next locality is the Red Seu. Limopsis aurita itself wa-s, until 



