出版者

公益社団法人 東京地学協会

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.125, no.2, pp.Cover02_01-Cover02_02, 2016

---

&emsp;かつて超大陸パンゲア西部の陸棚浅海や砂丘で堆積した古生代の地層がほぼ水平なまま隆起し,標高2,000 mの台地表面を飾っていることは驚きだ.隆起以前から存在したコロラド川は,大地の上昇に抗って,もともとの川筋を残したまま穿入蛇行を続けて,現在もV字谷を削っている.北米大陸直下にあるマントル上部の上昇流が急速隆起の原動力だが,この隆起が止まれば大峡谷の崖はすぐに浸食されはじめ,ただのつまらない緩斜面に急速に変わってしまうだろう.単独の急崖で多様な地質時代の地層を一目で見ることができるのは大きな魅力であるが,あの急な崖をつくる地層そのものが特異なわけでない.同じ地層がほとんど変形もせず延々と周辺地域の地下につながっているからである.<br>&emsp;日本人がグランドキャニオンを訪れる場合,米国西海岸南部からインターステーツ40号線(旧ルート66号線)を東に進み,途中で北に折れて,大峡谷の南側に出るコースが定番であろう.Mather Point展望台やBright Angel Trailheadに自動車横づけで,台地上からのあの絶景を眺めることができる.しかし,あえて崖沿いにさらに東に小一時間進むと,大峡谷東部のコロラド川上流部では谷幅が広がり,台地の上からも蛇行する川の流れが見える.夕闇迫る頃のDesert View展望台から,ちょっと趣の異なる光景を楽しむことができた.さらに,よく目をこらすと,水平な古生層最下部のカンブリア系と,その下の先カンブリア時代の岩石との間の明瞭な不整合(the Great Unconformityと呼ばれる)を目視できる.<br>(写真と説明:磯﨑行雄)

著者

小藤 文次郎

出版者

公益社団法人 東京地学協会

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.42, no.10, pp.562-563, 1930

著者

吉野 正敏

出版者

公益社団法人 東京地学協会

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.118, no.6, pp.1221-1236, 2009-12-25

参考文献数

60

被引用文献数

1 2

---

&emsp;The global climate is known to have been relatively warm during the period from the 4th to 10th centuries, although there were slightly different fluctuation patterns locally and regionally. The present article addresses these differences, analyzing the results of previous studies. The warm period is known in Europe as the Medieval Warm Period.<br>&emsp;Evidence in Japan is also found from the 4th century to the 11th century. Because historical age divisions differ between Europe and Japan, the peak of the Warm Period from the 7th to the 10th century is classified as part of the ancient period in Japan. Therefore, the Warm Period in Japan has been proposed to be called the Nara-Heian Warm Period, Heian Warm Period or Little Climatic Optimum.<br>&emsp;Based on the water level changes of Lake Shinji in Shimane Prefecture, the present article discusses the warmer climatic conditions in the Heian Period. It also examines old agricultural settlements in the Tohoku District, northern Honshu. People came from Hokkaido or northern Honshu and cultivated rice in the northeastern-most part of Honshu in the 1st century B.C. It is thought that the effect of the warm current branch flowing along the Japan Sea Coast and emerging on the Pacific side through the Tsugaru Straight had an influence on the distribution of rice cultivation at this early stage.<br>&emsp;Finally, the article shows that the northward shift of the power front of the Central Government (Yamato Chotei) during the 7th to the 9th centuries occurred about 70-80 years earlier in Dewa, an ancient state on the Japan Sea side of Tohoku District, than in Mutsu, also an ancient state on the Pacific side. It is interesting to note, however, that the speed of the northward shift was almost the same on both sides, even though there were different political powers, situations and problems on either side. It is suggested that the northward shift was affected by the warming on the broader space scale.

出版者

公益社団法人 東京地学協会

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.26, no.7, pp.565c, 1914

著者

零丁

出版者

公益社団法人 東京地学協会

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.11, no.7, pp.512-514, 1899

著者

町田 洋 新井 房夫

出版者

公益社団法人 東京地学協会

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.88, no.5, pp.313-330, 1979

被引用文献数

53 27

---

The eruptions of the Daisen Valcano (35&deg;22'N, 133&deg;33'E) were mainly rhyodacitic and of the paroxysmal type, producing several extensive sheets of tephra. The Kurayoshi pumice (DKP, for short), one of the excellent Late Pleistocene markers arising from the Daisen valcano, is rhyodacitic in composition with abundant hornblende and orthopyroxene crystals and relatively small amount of biotite. Its identification can be made from the above mentioned mineral assemblages as well as from the characteristic refractive index of orthopyroxene (&gamma;=1.703-1.708) and of hornblende (n<SUB>2</SUB> = 1.673-1.682) and the specific crystal habit of orthopyroxene. This pumice-fall deposit occurs on marine and fluvial terraces in the San'in and Hokuriku districts facing the Japan sea and extends eastward beyond the Northern Japan Alps to north Kanto plain as a thinner discontinuous layer. Stratigraphic relation with the dated tephra layers in north Kanto indicates that the pumice was probably deposited between about 47, 000 and 45, 000 years ago. That is, this pumiceous deposit is found at the intermediate horizon between Yunokuchi Pumice (UP, slightly younger than 49, 000 YBP) and Hassaki Pumice (HP, 40, 000-44, 000 YBP) in north Kanto, about 500 km far from the Daisen.<BR>Daisen Kurayoshi Pumice wonld be particularly valuable for establshing chronological framwork as a fundmental time-marker in arears where no suitable markers have yet been documented. Moranic deposit of the Murodo glacial advance at Mt. Tateyama, Northern Japan Alps, is mantled by this marker and overlies the Raicho-dai pumice-fall deposit, products of the earliest stage of volcanic activity of Tateyama III, which is correlated with the Omachi EPm deposit approximately 60, 000 years old. Distribution of these two unreworked tephras indicates that major valley glaciers had nearly disappeared by the times of these initial tephra falls. The glacial advance at Mt. Tateyama, the most extensive of the advances during Last Glacial age, therefore, apparently culminated between about 55, 000 and 50, 000 years ago. On the other hand, a filltop terrace repesented by Uwadan terrace along the River Joganji flowing from Mt. Tateyama, is covered by DKP and is nearly younger than the pyroclastic flow deposit of Tateyama III. Accumulation of the river of Uwadan stage is, therefore, simultaneous and probably associated with the Murodo glacial advance.

著者

新井 智一

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.114, no.5, pp.767-790, 2005-12-25

参考文献数

47

被引用文献数

2 1

---

This study examines the interaction between the politics in Fussa City and the Yokota Air Force Base, that is "the politics of place, " from a range of political, economic, and cultural processes which maintain the existence of the base.<BR>Military bases are generally established for global geopolitical purposes. However, the establishment of a military base has cultural implications for the local communities where the base is located, i.e., increased concerns about crimes committed by seavicepersons and noise by aircrafts. Although these military bases have some serious impacts, especially in Japan, geographers have not yet examined the issues regarding a particular military base and the resultant politics in the city.<BR>On the contrary, since the 1980s, Anglo-American political geographers have paid more attention to "the politics of place" This refers to the local politics that occur due to the interaction between a structural constraint and the individuality of a particular place.<BR>Therefore, this study examines "the politics of place" on the Yokota Air Base in Fussa City, Tokyo, by using resources from the local newspapers, novels, magazine articles, and council proceedings.<BR>The results are as follows : (1) Owing to the independence between the U.S. Air Force and local political and economic actors, an urban structure and local economy that depended on the Yokota Air Force Base were constructed in Fussa Town after the establishment of the base in 1945; (2) because of this structure, the local economy became to depend on Air Force personnel as consumers; (3) however, due to a shift to the floating exchanging rate and a reduction in the population of the base in the first half of the 1970s, there was a decrease in the influence that Air Force personnel had on the local economy; (4) since the 1980s, an economic agent utilized the "atmosphere" and "image" adjacent to the base to revitalize the local economy; (5) furthermore, the mass media represented Fussa City as a "base town" and conducted a review of the city in the 1960s, thus contributing to its revitalization; (6) during the economic slump in the 1970s, some local political agents were against the existence of the base. However, successive mayors of Fussa City have accepted the existence of the base, and utilized the subsidies it receives from the national government in order to construct the urban infrastructure.

著者

田近 英一

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.116, no.1, pp.79-94, 2007-02-25

参考文献数

86

被引用文献数

3 1

---

Liquid water on the surface of the Earth might have frozen entirely at least 3 times during the history of the Earth (650 Ma, 700 Ma, and 2.2 Ga). Assuming such extreme conditions, the snowball Earth hypothesis explains several unusual geological features associated with glacial deposits in the Proterozoic glaciations. Life should, however, have faced serious crises during these glaciations because liquid water is necessary for life. In particular, survival of photosynthetic algae, which are supposed to have appeared before the Neoproterozoic glaciations, might have been difficult if the surface water froze completely. There would have been refugia for life during the global glaciations. Life could have survived if the equatorial ocean was not completely frozen (soft-snowball condition), or equatorial sea ice might have been very thin (on the order of 10 meters). Even if these conditions were not achieved, life could have survived in shallow hot springs around volcanic islands. It would be much more difficult for eumetazoa to survive such severe conditions if they appeared before the Neoproterozoic glaciations as suggested by molecular clock studies. The appearance of eumetazoa after the last global glaciation (Marinoan glaciation), as suggested by the paleontological record, however, avoids this problem.

著者

加瀬 友喜

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.105, no.4, pp.512-525, 1996-08-25

参考文献数

18

著者

町田 洋 光谷 拓実

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.103, no.4, pp.424-425, 1994-08-25

被引用文献数

1 7

著者

川澄 隆明

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.103, no.3, pp.295-300, 1994-06-25

著者

Mori Jim 加納 靖之

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.118, no.3, pp.492-498, 2009-07-07

参考文献数

16

被引用文献数

1 9

---

2006年5月26日に発生したジョグジャカルタ地震による地震動が,250km離れたインドネシアのSidoarjo泥火山の噴出を誘発した可能性について検討した。この泥火山は2006年5月から噴出を続けている。泥火山の近傍で生じた流体圧変化と地震発生の時間的な一致から,地震波がこの地域の地下流体の状態に影響を与えたことが示唆される。別の同規模の地震のデータを用いて,地震波による応力変化の大きさを見積った。応力変化はごくわずか(0.005から0.010MPa)であったが,他の地域であればこの程度の応力変化でも微小地震を誘発した場合がある。地震の数分後に流体圧変化が生じたようであり,これは地下流体が地震動に対して応答したことを示していると考えられる。2006年ジョグジャカルタ地震は,Sidoarjo泥火山で小さな流体圧変化をひきおこした可能性があるが,これが泥火山の噴出開始に直接関係しているかどうか評価することは困難である。

著者

吉田 明夫

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.103, no.3, pp.201-206, 1994-06-25

被引用文献数

1 1

---

Correlation between earthquakes in Kanto region and intermediate-depth earthquakes in Hida region, central Japan is re-investigated. We found that a significant correlation exists between earthquakes with depth of 70 km and deeper in western Kanto and intermediate-depth earthquakes in Hida region, but such a correlation is not seen for earthquakes in eastern Kanto. This result shows that earthquakes occurring in the Pacific slab are well correlated each other, but earthquakes which occur in relation to the subduction of the Philippine Sea plate are not correlated with intermediate-depth earthquakes in the Pacific plate. Intermediate-depth earthquakes in Hida region have a tendency to precede earthquakes in western Kanto. This feature may be related to the dynamics of the plate motion which oceanic plate is pulled by the subducted slab.

著者

藤井 理行

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.114, no.3, pp.445-459, 2005-12-25

被引用文献数

4

---

This paper describes past climate and environmental changes during the past 101 to 105 year time scale obtained by recent studies on ice cores from Arctic and Antarctica. Shallow ice cores from Greenland and Svalbard show clear North Atlantic Oscillation (NAO) signals and explosive volcanic activities in the Northern Hemisphere and the equatorial regions. A deep ice core drilled to 2503 m at Dome Fuji, Antarctica covers the past 320 ka, which includes 3 glacial-interglacial cycles with Milankovitch cycles of about 20, 40, and 100 ka. Major chemical compositions and microparticle flux show high concentrations in glacials and low concentrations in interglain high-middle latitudes during glacial-interglacial cycles. The Dome Fuji deep ice core contains 25 visible tephra layers. An analysis of the chemical compositions shows the possible source volcanoes in and around the Antarctica.

著者

石橋 克彦

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.108, no.4, pp.399-423, 1999-08-25

被引用文献数

4 18

---

A large volume of historical documents in Japan show that great subduction earthquakes have repeatedly occurred along the Suruga-Nankai trough off southwest Japan since A.D. 684 with an interval of 100-200 years. They occurred as pairs of <I>M</I>8 events, one in the eastern half (Tokai earthquake) and another in the western half (Nankai earthquake), as was the case for the 1854 Ansei earthquakes, while sometimes occurring as single giant events like the 1707 Ho'ei earthquake. Although the space-time pattern of their recurrence is the best-known in the world, we should study more past events in order to understand the tectonophysical bases of their recurrence. In this respect I review the present understanding of historic Tokai and Nankai earthquakes and discuss related problems from the viewpoint of historical seismology. In this paper, the first of the three in all, I review the events until the early half of the 14th century. The keys to identifying older events are strong ground motion and damage in Kyoto, Nara, and Osaka, those in wider area of southwest Japan, tsunamis along the Pacific coasts of southwest Japan, typical coseismic vertical crustal movements of the Kochi plain, the Muroto and Oma'ezaki points, and the Ise and Suruga Bay coasts, temporal inactivity of specific hot springs, and aftershock activities recorded in Kyoto. The 684 Hakuho earthquake was definitely a Nankai event, and possibly included a Tokai event simultaneously (possibly Ho'ei type). The 887 Nin'na earthquake was also a definite Nankai event and was probably a Tokai event as well (Ho'ei type). The 1096 Eicho earthquake was clearly a Tokai event, but the following 1099 Kowa earthquake has some discrepancies that prevent it from being regarded as a <I>M</I>8 Nankai event. It is not clear yet whether great earthquakes occurred or not in the ca. 200 year intervals of 684-887 and 887-1096. It seems probable that great Tokai and Nankai earthquakes took place in the mid-13th century, but a more detailed investigation of historical seismology is required to discover the missing event.

著者

Radvanec Martin

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.118, no.4, pp.686-699, 2009-08-25

参考文献数

30

被引用文献数

2

---

この研究は,1945年8月6日,午前8時15分,広島の原子爆弾爆発による熱線の強力な影響を,2片の被爆瓦片を用いて研究したもので,この瓦片は元安川に架かる元安橋下流約100mの西岸で1977~1982年にかけて発掘されたものである。爆発から1.318秒後,爆心地で破壊された建物から衝撃波によって吹き飛ばされた大変熱くて融解した多数の破片は,元安川西岸に堆積した。この瓦片はおそらく,破壊された清病院の石塀,西向寺および(もしくは)西蓮寺からのもので,川の水で急激に冷却されたものと思われる。<br> 瓦片は安山岩質の火山砕屑岩からなり,その表面は3.18mmの深さまで融解していた。そのガラス質の層は,安山岩から玄武岩質安山岩の組成をもつ。これらはクリストバル石および/もしくはリンケイ石,ピジョン輝石(X_Fe = Fe/(Fe + Mg)= 0.37-0.44),角閃石(X_Fe = 0.33-0.42),曹灰長石(Ab_48.2-40.6An_51.8-55.5Or_0-3.9)およびK-長石(Ab_8.2Or_91.8)が融解生成したものである。融解が3.18mmの深さにまでおよんでいることと,上記鉱物質のそれぞれ異なる融点および溶融深度から,爆発後の爆心地の物体表面の温度6287℃が算出された。この表面温度は,深さ2.68~3.18mmの区間における残存鉱物と,溶融深度の関係から導き出した。回帰直線<i>T</i> = -1715.1<i>d</i> + 6287(<i>d</i>は深さ)(<i>R²</i> = 0.989)を外挿して求めたものである。安山岩瓦表層部の温度勾配は1mmあたり1715℃で,深さが2.86mmから3.18mmの間では,融解ガラス質と本来の鉱物質は等量である。3.64mm以下では,火山砕屑安山岩の構造および鉱物組成は,本来の組成を有している。

著者

鈴木 康弘 堤 浩之 渡辺 満久 植木 岳雪 奥村 晃史 後藤 秀昭 STREL'TSOV Mihail I. KOZHURIN Andrei I. BULGAKOV Rustam TERENTIEF Nikolai IVASHCHENKO Alexei I.

出版者

Tokyo Geographical Society

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.109, no.2, pp.311-317, 2000-04-25

被引用文献数

1 4

---

We have prepared a preliminary active fault map of Sakhalin, Russia, based on an interpretation of aerial photographs and satellite images. Major active structures include 110-km-long active faults along the western margin of the Yuzhno-Sakhalinsk Lowland in southern Sakhalin and 120-km-long active faults along the western margin of the Poronaysk Lowland in central Sakhalin. These active faults are parallel to but are located as far as 10 km east of the Tym-Poronaysk fault. Geomorphic surfaces on the upthrown side of the fault are tilting westward, therefore, the faults are considered to be west-dipping low-angle reverse faults. The vertical component of slip rates of these faults are >0.3 mm/yr in southern Sakhalin and 1.0-1.5 mm/yr in central Sakhalin. The net-slip rates could be much greater because the faults are low-angle reverse faults. If these faults rupture along their entire length during individual earthquakes, the earthquakes could be as great as M7.6-7.7. In northern Sakhalin, we have identified a series of right-lateral strike-slip faults, including the 1995 Neftegorsk earthquake fault. The slip rates for these faults are estimated at 4 mm/yr. The right-lateral shear in northern Sakhalin and east-west compression in central and southern Sakhalin may reflect relative plate motion in far-east Asian region.

著者

澤口 晋一

出版者

学術雑誌目次速報データベース由来

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.104, no.6, pp.874-894, 1995

被引用文献数

4 8

---

The rates and processes of periglacial mass movement were measured on the vegetation-free debris-mantled slopes in middle reaches of Adventdalen and Reindalen in central Spitsbergen Svalbard (Fig. 1). All slopes are mainly covered with debris of sandstone and shale of Jurassic, Cretaceous and Tertiary age (Fig. 2). A grain size analysis shows that surface layers of these slopes are composed of rubble and frost-susceptible fine materials (Fig. 5). The maximum depth of active layer varies year by year, but the average depth is estimated about 1 meter. Total 17 painted-stone lines were installed nearly horizontally on the slope surface in above 2 areas : 12 lines during the summer, 1988 and -5 during the summer, 1989 in order to detect movement rates of surface materials (Table 1). Eight pieces of flexible glass-fibre tubes (5 mm in diameter) were inserted into the ground vertically in 1988 and 1989. Furthermore measurement of year-round ground temperature and frost heave was achieved at north-facing mountain slope (700 m a.s.l.) of Mt. Skolten, using a data logger at 3-hour intervals from August, 1990 to July, 1991. Sensors were installed at 0, 5, 20, 40, 60 and 100cm in depth.<BR>Annual averages of movement rates measured by painted stone-lines are 0.6 cm to 11.2 cm (Table 1). Movement rates of surface rubble and slope gradients have roughly mutual relation (Fig. 3). Deformation of all painted stone-lines were patterns parallel to the base lines, and this occurred on every type of slope materials independently of the thickness and size of surface rubble layer (Fig. 4). The vertical velocity profiles of the excavated tubes fall into three types : straight profile keeping tilt (Fig. 6 JH-1), concave profile indicating the greatest movement at the surface (5-1, S-2, S-4, R-5) and complex (concave/convex) profile indicating relatively larger movement at depth (AD-4, S-3, R-3). The movement of the tops of all tubes averaging 3.4 cm, which similar to the average rate of movement measured by painted stones. This implies that these three types of deformation were formed by the same processes, namely frost creep and gelifluction.<BR>Only eleven diurnal freeze-thaw cycles were recorded at the ground surface on the northfacing mountain slope (19°) of Mt. Skolten from August, 1990 to July, 1991 (Fig. 7-a). Maximum and average depth of ground freezing occurred during these short-term cycles were 6.5 cm and 3.2 cm respectively. Frost heave recorded as the average 0.47 cm per 1 event, occurred from middle August to middle September, corresponding to the diurnal freeze-thaw cycles (Fig. 8). On the other hand, the heave caused by seasonal frost occurred from 21 to 27 August and the amount was 3.0cm (Fig. 8). The seasonal heave occurred untill the frost table reached less than 30cm in depth. The cumulative amount of diurnal and seasonal frost-heave is 8.7 cm. Accordingly amount of potential frost creep for the year is calculated to 2.7 cm on the 19 degrees slope. The annual average movement rate which was measured by painted stonelines at the same slope is 4.0 cm. This value is lager than the potential frost creep. Since the movement of painted stone-line resulted from a combination of frost creep and gelifluction, the value (1.3 cm) which deduct potential frost creep from movement by painted line is regarded as movement by gelifluction.<BR>An increase of thickness of surface rubble layer without interstitial fine materials is the cause of decrease of rubble movement because ice segregation do not occur in such rubble layer (Fig. 9). Especially the surface rubble attaining more than about 45 cm in thickness suddenly decrease in movement rates by the reason of the layer underlying such thick rubbles maintain the frozen conditions for all the year round.

著者

長岡 正利

出版者

公益社団法人 東京地学協会

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.93, no.4, pp.Plate1-Plate2, 1984

被引用文献数

2

著者

増田 隆一

出版者

公益社団法人 東京地学協会

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.105, no.3, pp.354-363, 1996-06-25

参考文献数

29

被引用文献数

1

---

The richness of fauna diversity is seen on the Japanese Islands, which range through 3, 000 km. When and from where have theanimals immigrated to Japan? Also, for understanding natural history of the Japanese Islands, it is very importantto investigate evolutinary history and origin of animals distributed on each island. While the evolutionary questions have been paleontologically and geologically examined so far, some of them are still unclear. Recent development of molecular phylogenetic study provides a reliable sight to understanding evolutionary history and origin of species. Advantageously, molecular study can analyze phylogeny of living species without fossil data.<BR>In Japan, two wildcats, the Iriomote cat and the Tsushima cat, live on the Iriomote Island and the Tsushima Island, respectively, where land bridges between the Asian continent and the Japanese Islands were present in the past time. To know evolution of these wildcats gives us useful information for better understanding of natural history of the Japanese Islands. Moreover, because both the wildcats are now endangered, it is now strongly needed to understand phylogenetic status of them for conservation and management. For the reason, we investigated molecular phylongeny of the two wildcats based on mitochondrial DNA sequences, and revealed that both the wildcats are very closely related to the leopard cat <I>Felis bengalensis</I>, which is widespread throughout Asia. Furthermore, from the DNA data, the Iriomote cat and the Tsushima cat were estimated to have diverged from the continental leopard cat approximately 200, 000 and 100, 000 years before present, respectively. The dates estimated by molecular data were in concordance with formation dates of the Ryukyu Arc and the Tsushima Island, respectively. These results suggest that geographic barrier has led fixation of some unique morphological characters into each cat population, while the two Japanese wildcats are still genetically close to the continental leopard cat.