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:::
Introduction
Earlier Geologic Maps of Taiwan
Geographic Setting
General Geology And Geologic Provinces Of Taiwan
Explanation Of Legend And Representation Of Geologic Data
Eastern Central Range
Western Central Range Backbone Ridges
Western Foothills
Eastern Coastal Range
Geology Of The Hengchun Peninsula
Major Geologic Features Of Taiwan
Plate Tectonic Setting
References


:::Geographic Setting
Taiwan lies about 150 kilometers off the Fukian coast of the China mainland. It is separated from the latter by the Taiwan Strait which has an average depth of 100 meters. The province of Taiwan is composed of 79 islands and islets. These are geographically represented by the main island proper, the thirteen islands and islets scattered around it, and the Penghu Island Group or the Pescadores. One remote island Tiaoyutai is nearly 150 kilometers north-northeast of the main island of Taiwan. These islands and islets rise abruptly from the margin of the continental shelf of Asia. East of the main island, submarine slopes plunge down to the Pacific Ocean at a grade of 1:10 and the ocean reaches a depth of more than 4,000 meters about 50 kilometers from the coast.
The main island of Taiwan is spindle-shaped, with the longitudinal axis ex-tending roughly north-south for a length of 385 kilometers. The maximum width is 143 kilometers. The island occupies a total area of 35,960 square kilometers. The Penghu Islands lie some 50 kilometers west of the main island. They comprise a group of sixty-four islands and islets with a combined area of about 127 square kilometers at low tide. Penghu is the largest island in the group, having an area of 64 square kilometers. The rest of the islands and islets in the Penghu Group are small and only eight of them have an area more than one square kilometer. Of the thirteen subordinate islands and islets surrounding the main island, Lutao, Lanhsu, and Kueishantao off the eastern coast of Taiwan are the three important islands and are populated. The reef-capped Liuchiuhsu island on the southwest of the main island of Taiwan is also populated.
The Central Range forms the backbone ridge and is the main water divide between the eastern and the western slopes of Taiwan. It separates Taiwan island into two unequal parts, the western flank being about twice as wide as the eastern flank. Consequently the stream gradients are much steeper on the east of the Central Range. The Central Range trends northerly for a length of 350 kilometers, with more than 25 summits exceeding 3,000 meters above sea level. One significant high range is distinguished to the west of the main backbone ridges of the Central Range. This is the geologically distinct Hsuehshan Range. The highest peak in this range is Hsuehshan (Mt. Sylvia), 3,885 meters above sea level. Yushan (Mt. Morrison) is the highest peak in the Central Range proper. It is 3,952 meters above sea level and is the highest mountain in the island groups on the western side of the Pacific Ocean.
The Central Range slopes westward into foothills and then into broad, elevated tablelands and uplifted terraces. A wide coastal plain extends southwest of this foothill region, bordering the Taiwan Strait on the east. This coastal plain has a north-south length of 240 kilometers and a maximum east-west width of 45 kilometers.
East of the Central Range is the Coastal Range. It is 140 kilometers long and 10 kilometers wide, with peaks ranging from 1,000 to 1,500 meters above sea level. The Coastal Range faces the Pacific Ocean to the east and is separated from the Central Range to the west by a longitudinal valley. This median valley has a length of about 150 kilometers and an average width of less than five kilometers.
Three prominent volcanic areas are known in Taiwan. The Tatun Volcano Group in the north is a group of volcanic cones composed largely of andesitic flows and pyroclastic deposits. These mountains, culminating in Chihsingshan at an elevation of 1,120 meters, form the rounded northern extremity of Taiwan. All the volcanoes in this group are dormant and are characterized by numerous fumaroles, solfataras, and hot springs, without any record of active eruption in historic times. The Penghu Islands represent a volcanic area of fissure eruptions. These islands and islets are marked by low flat-topped tablelands consisting of basalt flows and tuffs with minor sand and clay intercalations. The highest elevation in this island group is a little over 50 meters above sea level. The third volcanic area is the Chilung Volcano Group, consisting of scattered exposures of dacite that form several distinct ridges protruding out from Miocene strata on the northern coast east of Chilung city. Physiographically, little in the way of volcanic landforms can be distinguished. The dacite bodies could be shallow irregular intrusions or extrusions and are closely associated with the gold-copper deposits in that area.
For those readers who are not familiar with the geography of Taiwan, the index map of Taiwan in Fig. 1 shows major geographic features and subdivisions. The province of Taiwan is divided into sixteen hsien (prefectures) and five municipalities. The prefectures are: Taipei-hsien, Taoyuan-hsien, Hsinchu-hsien, Miaoli-hsien, Taichung-hsien, Changhua-hsien, Nantou-hsien, Yunlin-hsien, Chiayi-hsien, Tainan-hsien, Kaohsiung-hsien, Pingtung-hsien, Taitung-hsien, Hualien-hsien, Ilan-hsien, and Penghu-hsien. The five municipalities are Taipei, the largest city, followed in order by Kaohsiung, Tainan, Taichung, and Chilung. Tiaoyutai, the small islet about 150 kilometers northeast of the main island of Taiwan, is an offshore islet of Ilan-hsien, but is too remote and small to be shown on the index map
General map of Taiwan
Figure1. General map of Taiwan

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