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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


:::Explanation Of Legend And Representation Of Geologic Data
The 1974 geologic map of Taiwan, presented on a scale of 1:250,000, is divided into four sheets. It summarizes the results of geologic mapping in Taiwan since the 1:300,000 map was published in 1953. The rocks of Taiwan are divided into 37 separate units with additional symbols for limestone layers, coal beds, and tuff lenses. As compared with the older maps, a more detailed subdivision of the Neogene sediments into a larger number of rock units was made to illustrate the different geologic environments in the three geologic and tectonic provinces of Taiwan. Rocks of the same age in these three provinces are of different lithologic characters and structural features, and therefore are of different significance in the geologic development of Taiwan. They are represented by different units and color patterns in the legend so that a better understanding of the geology of Taiwan can be attained. This should be of value to those who use the geologic map for mineral exploration, earthquake or engineering studies, and other useful purposes. The subdivision of the rock units in the legend is based mainly on stratigraphic-lithologic sequences and not merely on the age of the rocks as most of the older maps did. These units are, therefore, chiefly cartographic units.
The legend is divided into two major divisions: sedimentary and metamorphic rocks, and igneous rocks. There are 29 units in the former division and eight units in the latter division. Except the mafic to ultramafic igneous rocks in eastern Taiwan and a small exposure of quartz porphyry in the Taiwan Strait, the main igneous rocks are volcanic rocks. Both central eruptions and fissure eruptions are known. Small and scattered tuff and lava lenses are placed in the host sedimentary formations depending on field association.
Most stratigraphic names in the legend are derived from those already defined in published literature and maps, and are well-known stratigraphic terms. Three of the stratigraphic names, however, are new and have not been previously described. It is necessary to validate these new formational names that make their first appearance in the legend of this map. Definition of the new formations or groups is given later in this explanatory text together with brief descriptions of the older names.
Although a good deal is now known of the broad aspects of the geology of Taiwan and precise data are available for many areas, there remains considerable uncertainty in some areas, especially in the more inaccessible parts of the Central Range where both the stratigraphy and the structure are little known. In a large part of the Central Range, representation of geologic data on the map is much generalized because of lack of detailed mapping or because the geology is imprecisely known. Inevitably the geologic data of some areas are dealt with in more detail than those of others. To guide the reader, a reliability diagram is added to the map. A mapping scale diagram is printed at the lower-right corner (No. 3 sheet) of this map, and illustrates the different scales of the original geologic maps used for the compilation of the present map. These scales range from 1:10,000 to 1:250,000. The reader may thus have some idea of the reliability of the data in different parts of the map.
The information and data on the map was derived from both published literature and unpublished articles. Some generalization was necessary in a number of areas in order to reconcile different interpretations of the geology by different authors. It was the responsibility of the chief compiler and the members of the editorial committee to screen the data from different sources and, where there are differences, to decide which should be used for the map compilation. In a compilation such as this, adoption of a particular point of view cannot be avoided. It is inevitable that some geologists will not fully agree with the views presented in this publication. However, this map represents the fruits of the work of a large number of field geologists in Taiwan as well as the general viewpoint of the editorial committee.
In the first edition (1974) of the 1:500,000 geologic map of Taiwan, a total of 26 stratigraphic units are presented in the legend. In this revised edition (1986) of the map, 30 stratigraphic units are given in the legend. The increase in number of units is necessary in view of the increasing and advanced stratigraphic knowledge of Taiwan. Some newly proposed and revised formational names that make their first appearance in the legend of this revised map need to be validated and well-established. They are defined and discussed more fully in this revised text.


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