Part-I)•\ On the Agematsu area lies in the Kiso district, Japan•\ By iViotoinitsu Nishio* Michio Kawahara** This paper presents the result of a geological study using photogeologic interpretation in the Agematsu area including the Kiso River basin. In Japan, the photogeologic interpretation have been studied only qualitatively, but the quantitative interpretation were not yet utilized fully in the photogeologic study. Both the methods of interpretation are very important equally in order to

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... the possibility and limit of photogeologic interpretation. So, we interpret airphotographs qualitatively and quantitatively in this study. We found and traced lineaments on airphotographs in detail, and checked these interpretations in the field. Joints, faults and fractures were measured and mapped on the ground, and drainages were traced on the topographic map (1 : 5, 000). The above mentioned elements were graphed separately each other and compared numerically. Consequently, these data indicated that (1) an avarage of about 55 % of the joint sets on the ground coincided with airphoto lineament sets, (2) about 70 % of the faults and fractures coincided with the distribution and orientation of airphoto lineaments, and (3) drainage frequency and density changed clearly according to rock types. Although we can not jump to such the conclusion that these results will fit to everywhere because of the complex geological structure in Japan, we found, on these data, that the photogeologic interpretation was very useful. We hope our studies will give some suggestions to photogeologists.