Elevation profiles at the Brenner Pass for a planned railway line

Elevation profiles at the Brenner Pass.

For several years the public journals have been discussing the feasibility of a railway line intended to connect Germany with Italy, the Mediterranean Sea with the North Sea, right through the eastern trunk of the Alps. The Lukmanier, the Splügen, the Malserheide, the Brenner Pass, and the mountain crests between Bruck, Rottenmann, and Aussee in Styria were suggested as transit points for such a rail link. It is not our intention to weigh the favorable or unfavorable conditions of these Alpine passes against one another for such an undertaking, much less to gauge their significance for commercial traffic; in what follows we merely provide the results of the observations that the Geognostic-Mining Association collected through its inspection of the land regarding the terrain and ground elevations between Rosenheim, the Brenner, and Verona. Technical experts may judge from this whether the construction of a railway along this section is feasible; we assure only that our statements of altitudes above sea level are based on barometric measurements carried out carefully with excellent Kapeller instruments, which agree almost precisely with the trigonometric surveys of the Imperial-Royal General Staff. Equally reliable are the distances between locations, which were furnished to us by the Imperial-Royal Provincial Directorate of Building.

The entire route from Rosenheim via the Brenner to Verona naturally divides into four sections. The first encompasses the Inn Valley from Rosenheim to Innsbruck; the second, the ascent from Innsbruck to the summit of the Brenner through the Wipp Valley; the third, the descent from the Brenner Pass to Bozen along the Eisack; and the fourth, finally, the Etsch Valley from Bozen to Verona.

If the elevation profile of the Inn Valley from Rosenheim to Innsbruck is compared with the altitudes of the larger lakes in the Bavarian plain (Staffelsee 2030', Kochelsee 1884', Tegernsee 2337', Chiemsee 1591 Vienna feet), it appears in a surprising manner that the Inn Valley, even at Innsbruck (1820 Vienna feet), lies lower than the surface of most of these water basins. The Inn Valley must therefore be regarded as an inlet reaching far into the mountains from the plain; for at no point does one find an abrupt, steplike elevation that could indicate a natural boundary or termination of the lowlands, and even the geognostic conditions correspond remarkably with those of the plain, as the same Tertiary formations with pitch-coal deposits and the same horizontal strata of Nagelfluh outcrop in the lowlands of the Inn Valley that form the soil of the Bavarian arable fields. The Inn Valley from Rosenheim to Innsbruck, 59,310' in length, shows the following elevations:

The total ascent from Rosenheim to Innsbruck therefore amounts to 468', which, distributed over a length of 59,310°, yields an average gradient of 13/137'' or not quite one line per fathom. Even on the stretch from Haidach to Brixlegg, in which the steepest incline occurs, it calculates for one fathom at only 8/47'' or two lines. The floor of the Inn Valley is wide throughout, swampy in only a few places, and nowhere threatened by dangerous torrents. The subsoil consists of alluvial gravel, which forms a solid base. The coal seam near Häring, which yields good pitch-coal in generous quantities, lies close against the valley floor, and extensive peat fields are found moreover near Kramsach and on the mid-mountain plateau between Vill and Lans near Innsbruck.

The second section comprises the route from Innsbruck to the summit of the Brenner and passes through the Wipp Valley. Here the ground elevation stands in the following relation to the station distances:

In this section, therefore, an ascent of the terrain of 2444' is associated with a road length of 21,000'°, and the mean elevation per fathom is thus 1 26/53'' or almost one and a half inches. The steepest part lies, according to the current state of the road, between Untergries and the Brennersee, where it climbs 2 3/14'' per fathom. The Wipp Valley, which together with its continuation, the Brenner Valley, cuts through the central Alpine chain, consists in its lowest part up to the confluence of the Ruetz brook with the Sill of a narrow rocky gorge spacious enough only for the valley stream. One step higher it gains in width and forms on the left side a terrace extending at fairly uniform height between the stream bed and the surface of the mid-mountain plateau of Mutters and Igls up to the Stephansbrücke. On the right side of the valley, this terrace becomes noticeable only around the Zenzenhof and extends into the almost level Arn Valley, which is separated from the Sill by a wooded cone and opens opposite Schönberg. Past the Stephansbrücke this terrace is lost; the Wipp Valley remains enclosed by steep slopes and only widens again near Matrei, where the elevation of the mid-mountain plateau is reached. It proceeds almost level until beyond Stafflach, but becomes narrower and steeper before and beyond Gries until the pass summit is attained. The slope directly on the left bank of the Sill up to the surface of the mid-mountain area between the Iselberg and Matrei consists mostly of older alluvial formations, coarse cobbles, sand, and loam, and in only a few places do the clay-mica schist or its intercalated limestones emerge from them. Between Matrei and Steinach on the same side, the limestones of the Waldraster Spitze drop down to the road and also cross the wide mouth of the Gschnitz Valley, which can readily be used for a detour to ease the subsequent incline. The rear part of the valley around Gries and up to the pass summit is formed again by varieties of clay-mica schist and intercalated limestones. The same rocks also form the right valley wall from the Brenner to Wilten and are covered by alluvium in only a few places. This slope would therefore offer greater stability to construction than the friable scree slopes below Schönberg, and would also allow the almost level Arn Valley to be utilized for the alignment of the railway.

The southern slope of the Brenner is distributed along the course of the Eisack down to its confluence with the Etsch near Bozen, descending by 3521' over a distance of 48,050°.

From this it will be observed that the greater gradient occurs in the section from the Brenner to Brixen, which encompasses an elevation difference of 2649' over a length of 22,756° (hence a mean gradient of 1 9/22'' per fathom). This ground elevation is, however, concentrated particularly at two valley steps, namely the climb from Brixen to Franzensfeste and that from Sterzing to the Brenner summit. The former amounts to about 600' over a length of 4250°, the latter to 1491' over a length of 7000°. The hilly terrain north of Brixen and the wide mouths of the Mareit and Pflersch valleys nevertheless allow wide detours to moderate these steep sections. From the post house on the Brenner to the inn at Schellenberg the Brenner Valley is spacious and only slightly inclined, but further toward Sterzing it becomes gorgelike and narrow along the Eisack. Rocks from the clay-mica schist group continue to form the valley walls. From Sterzing to Franzensfeste the gradient of the valley floor is low and features a slight step only above Mauls. The ground is frequently marshy and subject to flooding. Down to below Mauls the mountains consist of mica schist and hornblende schist; around Mittewald granite rises and surrounds the narrow gorge of Brixen. The hill country from Schabs to Brixen is a massive deposit of older alluvial formations.

From Brixen to the confluence of the Eisack near Bozen, the fairly uniform gradient amounts to only 872' over 25,300°, yielding an ascent of only 5/11'' per fathom. Here, however, the terrain is less favorable; for shortly below Klausen, where crystalline and schistose rocks terminate and quartz porphyry takes their place all the way to Bozen, the Eisack Valley narrows into a fissure between steep rock faces into which the side valleys open just as narrowly. On the sunlit side the porphyry is heavily weathered and friable, and moreover extensive masses of scree rest upon it in precipitous slopes, which is why this section suffers heavily from landslides. The shaded side has firmer ground, weathering is not so advanced there, and construction would thus find greater safety on that flank. On the Villanderer Alm there are extensive tracts of the finest peat.

The final section from Bozen to Verona forms the valley of the Etsch and offers elevation conditions just as favorable as the Inn Valley.

The entire route measures 83,320° and descends by only 586'. For one fathom of length, an average gradient of 2/27'' is calculated. Just like the Inn Valley, the Etsch Valley is an inlet of the plain and merges into it gradually and without any distinct boundary. The Etsch Valley merely lies lower than the Inn Valley to the same degree that the level of the Po is lower than that of the Danube in Bavaria (Bozen 73'; Innsbruck 1820'; Verona 157'; Munich 1611'). Into this inlet, too, the gray sandstones and marls that border the southern foot of the Alps have penetrated, covering the Alpine rocks, porphyries and sandstones, limestones and dolomites in the valley basins and on mountain heights. Most of the floor of the Etsch Valley is marshy or subject to flooding, and will offer secure ground for a railway undertaking only once the course of the Etsch is regulated. It would indeed be possible to combine the embankment of the railway with the dyking of the Etsch, thereby achieving two purposes at once.

From the board of the Geognostic-Mining Association for Tyrol and Vorarlberg.

Dr. Alphons v. Widmann, Director.

Dr. Stetter, Secretary.