The Northern Limestone Alps run from the alpine Rhine to the Viennese basin and were constructed from the remains of life forms in the primeval sea, with a high proportion of reef material and chalky mud.

Limestone and Dolomite, - called carbonates - were therefore deposited in layers (they are 'sedimentary' rocks) and did not rise from the bowels of the earth. In order to understand their geology one has to consider that today's mountains were folded upward in the course of millions of years and that they originally formed the seabed of the Thetys (broadly speaking, the ancestor of today's Mediterranean Sea). This tropical sea emerged as a result of the primitive continent 'Pangaea' being split open. It expanded to reach its greatest dimensions during the Mesozoic era. Most of the rocks were deposited in the Triassic and Jurassic periods - about 150 to 230 millions of years ago.

Today we know that the continents float on the red-hot liquid mantle of the earth like huge plates. Where plates collide, they fold to form mountains and huge masses of rock are thrust over each other.

The rock of the limestone Alps was thrust from the south over the central Alps (the Tauern, the slate Alps) and are therefore called 'over-thrust mountains'. In tectonic terms, the carbonates are the 'superior' layer resting on top of the greywacke zone (the oldest continental material from the ancient Earth). They are called the 'upper eastern-alpine over-thrust system'.

The rock types are mainly dolomite, Wetterstein and Dachstein limestone.

The Enns valley Alps are part of the northern High Limestone Alps that constitute one of the most impressive mountainous landscapes in Austria. In the west they are linked to the Warscheneck at the Haller Walls (Gt. Pyhrgas, 2,244 m). In the east they are subdivided into the massifs of the Gesaeuse mountains (Gt. Buchstein 2,224 m, Hochtor 2,369 m) and are separated from the Hochschwab group and the Eisenerz Alps by the Enns and the Erzbach. The Eisenerz Alps in the south are already part of the slate Alps (greywacke zone).

To the north of the High Limestone Alps the mountains gradually become lower and eventually merge into the foothills of the Limestone Alps. There, less than ten kilometres away from the Gesaeuse, the Limestone Alps National Park (Upper Austria) can be found. In the south, however, we see the abrupt transition from the bright limestone walls into the gentle, densely wooded hilltops of the greywacke zone, consisting of the much, much older slate and quartz. These materials originated from the ancient Earth (Palaeozoic era) and are rich in mineral deposits as well as other mineral resources. The Erzberg provides an impressive illustration of this.

The Gesaeuse mountains are the eastern portion of the Ennstal Alps and are, essentially, an example of a cordillera. As such they represent something of a peculiarity in eastern Austria. In other places, the plateau mountains dominate, as in the Totes Gebirge or the Hochschwab.

The predominant rock type in the Gesaeuse mountains is the Dachstein limestone, deposited in the lagoons and behind the coral reefs of the Upper Triassic era. The Hochtor group's astonishing range of walls as well as those of the Buchstein's, are built from it. As already mentioned, above the rock walls there are also the remnants of plateaus, which, because of the karst topography, often present a rather bizarre picture.

The base of the great mountain walls is mostly composed of the brittle Wetterstein dolomite, that was deposited in the large and monotonous ocean basins of the mid-Triassic era, as mentioned above. Though hated by the mountaineers, it is the characteristic feature in the Johnsbach valley or in the Hinterwinkel. Due to the dolomite's deep fissures, weathering is intense, and this produces bizarre rock formations. The needles of rock often have an apparently human shape ('school master', 'crook backed tailor'). Between them are broad and bright streams amongst the detritus, rolling downwards into the valley. During thunderstorms these change into dangerous mudflows that can bury roads and railway lines within seconds.

As a transitional rock between the dolomite and the limestone we have the "Dachstein dolomite", which contributes to the composition of the mountains in the area of the Buchstein and the Planspitze. What catches the eye is the small "Raibl layer" between the Wetterstein and the Dachstein dolomite: a distinctive succession of brown sandstone, black slate and mottled dolomite. Often you see it at springs, at cliffs or in a change of vegetation. The boundary between the Dachstein dolomite and the limestone strata, is gradual rather than abrupt. Only by degrees did magnesium become increasingly scarce in the chemical environment. The Dachstein limestone is extraordinarily pure.

As we climb the mountains, so we move forwards in the Earth's geological history. Even so, we still keep the limestones. The start of the Jurassic era is characterized by red and partly mottled limes. The Lias limestone in particular strikes a special note in the idyllic high valleys. Here the Jurassic limestone and the 'flecked marl' (another of the sedimentary rocks) have a higher clay content than the Dachstein limestone and so, after weathering, they produce a deeper soil. (At the time of the first formation of mountains the ocean Thetys was 'squeezed together', and so there were significantly more alluvial deposits from the land; these deposits are also partly accounted for by the formation of islands). Following their best instincts people in the Middle Ages, cleared the high alpine pastures in these areas.

Younger rocks than these are hardly to be found in the Gesaeuse mountains. Over a long period of time they have been worn away by weathering and erosion. Strangely enough, on the plateaus and even up on the highest summits one can time and again find mottled bituminous clay soil or even strata of fluvial gravel. The "Augensteine" (the local name for pieces of highly polished translucent or transparent quartz) and the "Augenstein soil" are relics of the Tertiary era and therefore of the time when what is now the Gesaeuse National Park was still rolling country with a subtropical climate and northward flowing rivers.

The long cold 'night' of the Quarternary era - the Ice Ages - gave the last polish to the mountains, as the various corries show (Rossschweif, Sulzkar,…), and in, front of its mighty glaciers, left an impressive series of moraines (for example near Gstatterboden) and gravel terraces (Waag at Hieflau). The deeply excoriated valley of the Enns, upstream from the Gesaeuse, was successively filled up with gravel and lake clay at the end of the Ice Age. So it was that a chain of moors could develop there (Frauenberg Moor, Puergschachen Moor, Woerschach Moor,...).