APPLICATIONS OF THE THEORY OF MODERN STRATIGRAPHY TO REFORM THE METHOD FOR GEOLOGICAL MAP MAKING IN CHINA

The present method for geological map making in China is preparation of the system map in the field. No formation map has been prepared in China. Two kinds of geological maps are now in vogue in most countries; they are the formation map and the system map. The former takes account of geological formations, as exemplified by the folio sheets of the Geological Atlas of Chao County. In this geological atlas each formation is given a dis- tinct colour or pattern. For the production of such maps, large-scale base maps are needed, those used by us being mostly on a scale of 1:50,000, or approxi- mately 1 cm to 0.5 km. The system map aims to show in distinctive colour only geologic systems, each of which has a distinct colour pattern. All the subdivi- sions or a system are generally grouped together by the same tint, e. g. green and brown. The example is the Geological Map of the People’s Republic of China （1:4,000,000）. A question is often asked: should regional geologic maps express primarily formations or systems? In other words, should map making be based on rock formations or on time units? The decision is generally in favour of mapping rock units or formations. This method is apparently the most satisfactory, since all the mappable features, such as outcrops and topography, are the direct consequence of the rock formations and have no regard whatsoever to time relations. The present outcrops only show the present areal extent of a formation, and give no clue to the previous areeal extent of the strata depos- ited during a given time interval. So formation maps are the basic reference materials for the national economy and construction as well as land reclama- tion. The author suggests that the old method for geological map making, i. e. surveying in the field for making system maps, should be reformed; instead, formations should be adopted as the cartographic unit and mapping conducted on a lithic unit; that is to say, one should conduct formation map- ping in the field and prepare system maps in the office.