important peaks are Skalata, Small and Big Skakavets, Rilets; there are 28 peaks over 2,100 m. This subdivision is renowned mainly for the glacial lakes Ribni, Dzhendemski, Manastirski, as well as the largest glacial lake in the Balkan Peninsula — Smradlivo Lake. Northwest Rila, known also as Malyovitsa Rila, occupies about 24% of Rila and is situated between the valleys of Rilska to the south, Levi Iskar to the east, Samokov to the north-east and Dupnitsa to the west. Its much lower northern section is called Lakatitska Rila. It is linked with the Verila mountain range to the north through the Klisura Saddle, and with Central Rila to the east through the Kobilino Branishte saddle. The average elevation is 1,556 m; the highest summit is Mount Golyiam Kupen at an elevation of 2731 m. There are 29 peaks over 2,100 m. This subdivision is known for its rugged peaks and picturesque lakes in the Alpine zone that include the Seven Rila Lakes and the Urdini Lakes. Central Rila includes the mountain's highest waterfall, Skakavitsa (70 m). Southwest Rila stretches between the valleys of the Rilska, Iliyna and Belishka rivers to the north, the Predel Saddle that separates it from Pirin to the south, and Simitli and Blagoevgrad valleys to the west. It covers about 30% of the area of the mountain range. With an average elevation of 1,307 m, it has the lowest elevation in Rila. The highest summit is Angelov Peak (2,643 m). The Blagoevgradska Bistritsa River divides it in two distinct ridges to the north and to the south. Apart from its northernmost part, Southwest Rila does not have the Alpine character of the other three subdivisions. The biosphere reserve Parangalitsa is situated there. Geology, relief and summits Rila is a fault-block mountain and represents a crescent-shaped horst with two fault systems — concentric and radial. It is part of the oldest land in the Balkans, the Macedonian–Thracian Massif. The mountain range is formed mainly by metamorphic and intrusive rocks. The core of Rila is built up predominantly by granite. It is covered by a thick layer of crystalline schists and granite–gneiss; this layer is topped by sandstones and conglomerates which were formed by elevated Tertiary sediments. Traces of these sediments are found in the Northwest Rila at an elevation of up to 1,900 m. The highest zones are made mainly of granite, and below are crystalline schists,