GEOLOGY OF THE MT. GAUSTA REGION IN TELEMARK, NORWAY BY DOROTHY WYCKO FF WITH 5 MAPS AND 19 PHOTS. IN THE TEXT Introduction. Location and Geography of Telemark. Telemark Fylke 1 is the section of south-central Norway which includes the drainage basins emptying into the Skiensfjord2, as well as the land around the large !akes Nisservatn 3 and Fyres vatn. These !akes dra in into the Nid elv 4, a river flowing to the sea through Aust-Agder, the next fylke to the southeast. Telemark is irregular in shape, but the greater part of it Iies between 59° and 60o north latitude, and 71/zo and 91/zo longitude east of Greenwich. The narrow coastal strip of Telemark includes several towns - Skien, Porsgrund, Kragerø and Brevik. In the northern part, how­ ever, the only towns of considerable size are Notodden, on the Heddalsvatn and Rjukan, in the Vestfjorddal5 west of Tinnsjø6. Telemark is not crossed by any great continuous valleys, like those which form the main thoroughfares of many other sections of Norway. The drainage system is complex, with many large and small !akes, bogs and streams, cutting the country into a confused network of valleys. The farms are most! y grouped in grender 7, and communication with grender in nearby valleys, and with the outside world, is in many places roundabout and difficult. The popu­ lation of the moors and uplands is sparse. There are a few little l fylke -- a political division of the country, corresponding roughl y to state. 2 -fjord- as used in Norway means any enclosed arm of the sea - a bay or inlet; it is also used for large !akes. 3 -vatn - water, lake. 4 -elv - river. � -dal- valley. G -sjø -- sea, (large) lake. grend (pl.grender)- a gr o up of farms, neighb orhood; less compact !han a vill age. Norsk geo\. tidsskr. XIII. l 2 DOROTHY WYCKOFF farms in some of the upper valleys; but over wide tracts of the mountains there are no permanent settlements at all. For a few weeks in midsummer, peasants live in the rude seters 1, pasturing their cattle on the high levels; in September they return to their homes in the valleys. The mountains of southern Telemark are relatively low and, where they do not rise above the tree-line (900-1000 meters above sea leve!), are for the most part covered with forests of spruce, pine and birch. Farther north, the mountains show steep sides and rounded tops of bare rock; but some of the higher ones- e. g. Gaustafjell2 ( 1883 meters3) and Vindeggen ( 1492 meters 4)- are topped by steep narrow ridges, where snow Iies through most of the year. Early Descriptions. Telemark is a part of Norway in which systematic mmmg was very early begun, the copper and silver mine at "Sundzberg" - probably Sundsbarm in Seljord - having been chartered in 1524. A few geologica1 items are included in LUND's "Description of Upper Telemark in Norway"5. WILLE'S "Description of the Parish of Seljord"6 (which was at the time considered a model of local de­ scription, and is still a valuable source book for those interested in the antiquities, customs, and superstitions of Telemark) also contains chapters on natura! history, in which the author gives his observations on rocks, soils, mines, caves, etc. The first geologist to visit the regions was the German, NAUMANN, who travelled and studied in Scandinavia in 1821-22; but since he went through Telemark in May, when there was still much snow, his observations are too incomplete to be of great value. His book was published in 1824 7. I seter - a summer dairy-farm, like the chalets of Switzerland. 2 �fjell - mountain. 3 New measurement (1923-24) by Den Geografiske Opmåling, Oslo. Sheet 35. 3,9. 4 HELLAND, AMUND, Norges Land og Folk, Bratsberg Amt, p. 27, Kristiania, 1900. 5 LuND, jo HAN MICHAEL, Forsøg til Beskrivelse over Øvre Tele marken i Norge, Kjøbenhavn, 1785. o WILLE, HANS jACOB, Beskrivelse over Sillejords Præstegield, Kjøbenhavn, 1786. 7 NAUMANN, C. F., Beitrage zur Kentniss Norwegens, Leipzig, 1824. • GEOLOGY OF THE MT. GAUSTA REGION IN TELEMARK 3 u; "' Q) ..c:: t: o z o ..c:: 0.. 4 DOROTHY WYCKOFF Meanwhile the Norwegian geologist KEILHAU had also travelled through Telemark, and published a pa per 1 dealing particularly with the rocks which were later to be calied the "Telemark Forma ti on". As WERENSKIOLD remarks2, "The fact that KEILHAU so early began to study the geology of Telemark certainly had a great influence on all his peculiar conceptions of the mountainbuilding of Scandinavia - in few places does one find such thorough and intense metamorphism, at !east in southern Norway. All kinds of rocks seem to grade into each other; this supported KEILHAU's 'Transmutation doctrine'3". Since KEILHAU's time numerous geologists have visited the region. The more important papers which endeaver to unravel the question of the origin and history of the "Telemark formation" may be divided in to two groups: l. Those dealing with the relation of the whole "Telemark formation" to the pre-Cambrian formations in other parts of Scandi­ navia or Fennoscandia. 2. Those concerned with the separation of different members within the "Telemark formation", and the determination of their relations to each other. The Scandinavian pre-Cambrian. In Finland and in southern Sweden pre-Cambrian rocks are continuously exposed over great areas. The earliest Swedish geo­ logists distinguished two types: to the west, the "iron gneiss'', a strongly compressed metamorphic red granite containing small grains of magnetite (whence its name); and farther east, a series of less altered granites, porphyries and tuffs -- the "granite-leptites". In the zone of intense metamorphism between the two, and in the "iron gneiss'' near this zone, occur intrusive masses of hyperites -- elon­ gated patches which are parallel to the general strike of the gneiss. For some time it was believed that the "sharp" contact between these t KEILHAU , B. M., Om de Skandinaviske Formationers Anden Suite: Mag. f. Naturv. bd. l, 1823. Å 2 WERENSKIOLD, WERNER, Om Øst-Telemarken: N. G. U. nr. 53, rbok for ]909, p. Il, 1910. 3 KEILHAU'S theories are full y expressed in his book: Gaea Norwegica, Kristi­ ania, 1838, !850. GEOLOGY OF THE MT. GAUSTA REGION IN TELEMARK 5 two areas must be marked by a fault line 1: but with more detailed mapping the contact was found to be not "sharp" but transitional. DE GEER2 then proposed the explanation that the highly meta­ morphosed border zone is the result of an ancient period of mountain­ building: the "iron gneiss" and the "granite-leptite" series were originally rocks of the same type, but the former has been subjected to more intense metamorphism than the latter. The hyperites were forced up in to fissures formed during the mountain-building; the fact that they now appear less metamorphosed than the surrounding rocks is due to their great thickness which made them resistant to crushing, except peripherally. This hypothesis was combatted by T6RNEBOHM 3, who argued that the greater metamorphism of the "iron gneiss" in­ dicated that it must be the older formation, probably representing the "basement complex" upon which the "granite-leptites" had been laid down. DE GEER's explanation, however, won a general acceptance among Swedish geologists, though the age of the mountain chain (which DE GEER ascribed to the Algonkian) is still a matter of dispute4. In any case, it is possible that such a mountain chain had some relation to the continental landmass which is supposed to have existed to the south of Scandinavia in earl y Cambriam or previous time 5. BuGGE 6 has attempted to carry over this system of correlation into the Norwegian pre-Cambrian. In Norway the study of the most ancient rocks is more difficult than in Sweden. The two areas where pre-Cambrian rocks are exposed in southern Norway are separated from each other by the "sparagmite formation'' (the earliest Paleozoic sediments), and by the region of the Oslofjord, with its I NATHORST, A. G. , Ett forsok att fOrklara orsaken til! den skarpa gransen mellan sodra Sveriges vestra och ostra urterritorium: G. F. F., bd. 8, p. 95, 1886. BACKSTROM, H., Vestanåfaltet, en petrografisk studie: K.V. A., hand!., bd. 29, nr. 4, p. 104, 1897. 2 DE GEER, G., Om Algonkisk Bergveckning inom Fenn oskandias gransområden: G. F. F., bd. 21. nr.198, 1899. 3 ToRNEBOHM, A. E., Discussion, Jan. 4, 1900, of Prof. DE GEER's lecture of Dec. 7: G. F. F., bd. 22, p. 116, i 800. 4 TORNEBOHM, loe. cit. HoGBOHM, A. G., Pre-Cambrian Geology of Sweden: Bull. Geo!. Inst ., Upsala, bd. 10, p. 59, 1910. s BRøGGER, W. C., Norges Geologi: Norge 1814-1914, p. 199,200. 6 BuGGE, ARNE, Et Forsøk på lnddeling av det Syd-norske Grundfjeld: N. G. U., nr. 95, 1 92'2. 6 DOROTHY WYCKOFF faults and post-Silurian igneous rocks; and they are likewise se­ parated from the pre-Cambrian rocks in western and northern Norway by the central mountain chain, of Caledonian age. It has therefore become the custom to speak of a number of "formations" : the "Bamble formation", the "Telemark formation", the "Modum forma­ tion" and the gneisses of Smålenene. The Smålenene gneisses, southeast and east of Oslo, are con­ tinuous with the gneisses of southwest Sweden, and have always been considered to belong with them 1• West of the Oslo region, strongly metamorphic gneisses are found in two areas: o ne at Kongsberg, extending northeastward to Gran and Lake Mjøsen; the other in a stri p along the south coast, from Bamle to Kristiansand S.