要　旨　埼玉平野北西縁部の児玉丘陵の北東部には，多摩面を構成する浅見山礫層が分布する．浅見山礫層の礫種構成は，児玉丘陵の南縁を流れる小山川の河床礫のそれと著しく異なる．その礫種はむしろ，上武山地南側の荒川水系にある秩父盆地の段丘構成層と対比できる．

キーワード：高位段丘，児玉丘陵，浅見山礫層，尾田蒔礫層，礫種，上武山地，古小山川

---

図7．浅見山礫層・尾田蒔礫層・現河床礫の礫種構成． 1：石英閃緑岩，2：ホルンフェルス，3：砂岩（中・古生界），4：粘板岩（中・古生界）， 5：チャート，6：石灰岩，7：緑色岩，8：結晶片岩，9：中新統，10：安山岩．

---

Gravel kind Comparison in Higher Terrace Deposits at Chichibu
and Kodama Region in Saitama Prefecture, Japan

Kiichi OBATA
Saitama Museum of Natural History
Nagatoro Chichibu-gun, Saitama, 369-1305 Japan
Kikuji MATSUOKA
Toyooka High School
1-15-1 Toyooka Iruma-shi, Saitama, 358-0003 Japan
Fumitaka KUTSUMA
Kawagoe Hatsukari High School
2564 Suna-shinden Kawagoe-shi, Saitama, 350-1137 Japan
Masaichi RIKITA
Department of Science and Engineering, Waseda University
3-4-1 Okubo, Shinju-ku Tokyo, 169-0072 Japan
and
Fumio TSUNODA
Department of Engineering, Saitama University
255 Shimo-Okubo, Saitama-shi, Saitama, 338-0825 Japan

Abstract
　　The Middle Pleistocene Asamiyama gravel bed is distributed on the north of the Jobu mountains trending in a northeasterly direction. We can find a lot of boulder gravels of quartz diorite and various Jurassic sedimentary rocks in this polygenetic gravel bed. As exposures of these boulders are confined to areas where is on the opposite side of Jobu mountains, it is supposed that they were transported from the Chichibu Basin and adjacent areas. Moreover, on the basis of its components this terrace deposits is surely correlated with the Odamaki gravel bed in the Chichibu Basin along the Ara River. Accordingly, these gravel beds must have consisted of a sequence of the Paleo Ara Alluvial Fan which strikes south to north in earlist Middle Pleistocene time. This fan must have divided into two parts by upheaval of the Jobu mountains during late Middle Pleistocene, and the Ara River here turned eastward.