12 



next to tlic (loore of existing lionsos, or witliin a villum.', or next tu tlic liiiul- 

 ing-]iliiccs of tislicnnen, there is indeed pcarcely any daiij;er of a mistake lnOng 

 made; but whenever they are foiuid in n coinjKirativoly desert jilaoe and at a 

 larger distance from the sea, we are iiuloed forced to ix'serve our verdict until an 

 accurate investigation of the nioiwid has Ijccn made, and a tliorough kno\vle«lge 

 of all remnants of {K)ttcry and otlicr hranches of induitry contained in it ]inn 

 been obtained. There may be c;ise.s where even native tertiary phell layer» are 

 not easily distinguished from arlilicial shcll-lM'u|w. Tiiin difllcully i» greatest 

 whenever we are to deal with such inirls of thfwr Hheli-layei-s as have licen 

 washed away by tho recent sea and therefore, though of tertiary origin, are no 

 longer contained in tertiary strata, but in alluvial strata, into which they havu 

 lit-en newly and iiosthnmously imbedded. This, indeed, is the case with a grewl 

 many accumulations of shells along the kise of the ancient blutV-lino at I'ycno, 

 Oji, and other parts of Tokio and ila suburl«, where we find shell« of tho mme 

 description and of the same sjiecies as in the more ancient and deep shell layora 

 of Oji. 8urngadiii &c., under tho soil of the rice-fields, spread along tho l«.'^' of 

 the diluvial hills. This origin of the shell de|Hjsits fuimd in tlio.s4! pliu *.mi in 

 indoetl rendered obvious by tho occurrence of undoubto<lly tertiary layer» in their 

 close vicinity and by the absence of any other catise wliich could afford the shell». 

 But in such localities, as for inetanco on the southern side of the Yokoh;«un- 

 blufls, where the waves of the sea come actually into close eont;icl with the Who 

 of the bhiff, or at least very near it, it is sometimes im|)08sible to dniw a certain 

 distinct limit l)etween recent shells and tertiary shells <le]iositcd in a secondary 

 way by the torrents, breakers and waves of the jiR'sent ai,'e. Wo may aid, 

 liowcver, that in such cases this distinction is generally of slight iini>ortaneo and 

 serves only to make still inoiv evident the necessity of utmost aocuraey in all 

 those researches which Concern alluvial shell-deposit.-*. 



If we try to classify the alluvial formation, we may jirocecd in two way», 

 either arranging them simply according to their chemical and minonilogioil 

 qualities, or according to their geological age or com|Mrativo antiipiity. In tho 

 first case, we are to seiiarate tho clayish and sometimes somewhat e^tlcnn'ons 

 deposits of compamtively calm and stagnant water, together with the |>e«t- 

 dejxjsits made in perfectly stagnant water, from tho sand deposit« of rivers 

 running with some rapidity, or of the shore of a muglier sea. Wo m.iy sny 

 indeed, that the minerals contained in the rorks from whose ch-stru.tion tho 

 alluvial depo.sitji have been formed, are not without inlhience on the nature of 

 these de|>oäits (the magnetic-iron sands of the eastern coast being a striking 

 example of this influence), yet the minerals forming the gniiter jiarl of »ho»« 

 scHliments— quartz and common clay together with some limo — occur in almost 

 every kind of rocks and are .-carcely wanting in .-iny locality. We see, thenfoiv, 

 that modilications produced by the action of water are of tho «rnitest im|)ortanoo 

 for tho constitution of any seiliment, and serve aUive all to »ever the diffenuit 

 sorts of bulk and weiglit, causing in one instance coorsc snnds or even winjjKv 



