Along the shoreline of Lake Nojiri which is located among the volcanoes at the northernmost part of the Fuji Volcanic Zone and the upper course of the River Torii, there is noticed the distridution of lacustrine terraces that are separated by a low divide at Kumagura (Fig. 1). The writer observed at Furuma the fossil lacustrine terrace which contains a considerble number of lacustrine diatom fossils (Fig. 2, Tab. 1). The change of these fossil species in the stratal parts from A to C suggests that the old lake had been gradually filled up, and the peat bed of D containing Eunotia pectinalis seems to indicate the deposits at the shallowest stage of the lake. However, the occurence of clay and of fossils such as Synedra ulna and Gomphonema parvulum in E and F likely show that the lake level had relatively risen. Topographically to say, the middle course of the River Torii flows down through the mudflow district (Fig. 3). It is regarded that these lake deposits made the present topography resulting as overflow of lake water and that the Palaeo-lake level of “Furuma Fossil Lake” was about 675m above sea level. It is presumable that this fossil lake was a part of “Palaeo-lake Madarao” at the age of deposits of A-D in the Furuma fossil terrace and that the River Torii supplied much water to, that lake, judging from the topography in which the ancient outlet was so deeply dissected against the poor inlets on the present-day shore of Lake Nojiri. Considering from the altitudes of the ancient outlet, of the old shoreline and of the peat deposits, in that age the level of “Palaeo-lake Madarao” might have been about 665 meters. After that time the “Palaeo-lake Madarao” might have been separated into two parts at Kumagura by the Nagahara lava flow. One of them became the “Furuma (Fossil) Lake”, the level of which then rose and overflowed as the River Torii, and another became the “Palaeo-lake Nojiri” that changed its outlet as the River Ikejiri in a later stage (Fig. 4). Therefore, present-day Lake Nojiri may be considered as a remnant of both lakes of “Palaeo-Madarao” and “Palaeo-Nojiri”.