Тиетта. 2011, N 3 (17).

Рис. 1. Местоположение района Пюха-Луосто. Fig. 1. The location of the Pyha - Luosto area. and aesthetic value. It consists of about 2 billion old quartzite and conglomerate, which were formed as much older bedrock weathered and the sediments were deposited, then underwent metamorphism during an orogeny (Mielikainen 1979, Rasanen and Makela 1988). It is a residual mountain that has re­ sisted millions of years of erosion better than the sur­ rounding rock types. The conglomerate deposit can be seen every­ where like a belt around the lower southern slope of the mountain range. It is rhytmically bedded, con­ sisting in many places of tens of metres thick pebble beds. Most of the pebbles are round, the largest ones up to half a metre in diameter. They reflect a power­ ful stream in an ancient river, which transported the pebbles, wearing and rounding them. The rock type conglomerate is like a rock museum with samples of older bedrock in its pebbles. They come from rock types in the surrounding area, such as quartz veins and granite. In places, conspicuous red jasper can be found, forming small rounded fragments. Grey quartzite forms the upper slopes and tops of the mountain range. Originally the quartz- ite was quartz sand, sorted by running water, then got its present appearance by undergoing metamor­ phism. The quartzite layers form about one metre- thick beds. Horizontal or oblique series of beds al­ ternate. In the horizontal beds precipitate structures and ripple marks can be found. They are often just as distinct and astonishingly well preserved as the rip­ ple marks on present-day lakeside beaches. The rip­ ple marks of the quartzites are a structural souvenir from an ancient beach, swept by the waves of a sea or a lake. They also show clearly that the original sedi­ ment deposited in shallow shore water (Fig.2). Dendrites, branched precipitations of iron and manganese, can also be found. Crystalline quartz is rare and generally only occurs in cracks and on the walls of hollows in the bedrock. Such euhedral quartz Рис. 2. Волнистые отметины на кварцитовом валуне. Fig. 2. Ripple marks on the quartzite boulder. crystals are usually long and hexagonal prisms end­ ing in pyramid-formed surfaces. Some quartz veins contain more unusual colour varieties, including rosy quartz, smoky quartz and amethyst. Glacial meltwater processes cut scars in the mountain ridge Rugged canyons and gorges divide the moun­ tain range like huge cuts into several tops. Isokuru, the most remarkable canyon, with a depth of 220 metres, is Finland's deepest (Fig. 3). About two kil­ ometres further west lies a similar canyon, named Pikkukuru, with a depth of 130 metres. The floors are covered by rocks and blocks from the steep walls. At Peurakuru, which is a 50 metres deep canyon with a very rocky floor, the meltwater flowed in a tunnel at the base of the ice, eroding a subglacial gorge in the bottom of the tunnel. Loose material, partly from the gorge, was sorted and accumulated by the meltwater stream at its mouth in the form of the Peuraharju es- ker. Peuraharju is a subglacial esker, which consists of rounded pebbles and gravel washed by a powerful meltwater stream. Typically for an esker formed in a meltwater tunnel, it has steep sides and a sharp crest (cf. Johansson et al. 1995). The formation of deep canyons was influenced by weakness zones in the bedrock, where deep frac­ turing had occurred due to movements in the Earth's crust millions of years before the Ice Age. During the Quaternary period ice lobes caused effective erosion and plucked blocks off the fractured bedrock. Finally meltwater streams cleaned the canyon floors, carry­ ing away loose rock material and spreading it at the canyon mouths, accumulating gravelly outwash fans. Kettle holes are found on their surfaces, tens of me­ tres in diameter and several metres deep, formed as ice blocks transported by the meltwater stream were buried in the gravel. As the ice slowly melted, the gravel overlying it caved in, forming the kettle holes. Parallel lateral drainage channels run gently sloping down on the slopes of the Luosto moun­ 2