First part of a final report describing "efforts to confirm the existence and nature of clay seams in the [Vaiont Slide] mass and to confirm the possible existence of an 'old' slide at the site. These efforts were made by (a) firsthand field observations of the geology, (b) an examination of preslide and postslide airphotographs, (c) laboratory testing of samples of failure plane materials, and (d) and examination and translation of geologic and other documents related to preslide and postslide conditions" (abstract, para. 2). The report also presents stability analyses of the Vaiont Slide.