4. Isar - gemstones and fossils

When the water level allowes it, we go down to the Isarbed. For the next 150 meters, our path runs along the gravel bank, right by the water. Now we stand at the „Gries“. We will take time to go on a treasure hunt. In fact there are gemstones and fossils!

From far away the stones all look similar but if you have a closer look you will find something special. If it rains or after a rain shower the stones are shining and look especially beautiful.

Let`s take the stones in our hand and have a look at them.

Can you see the different?

The differents invite us to ask how they were formed.

Most of the stones are white, light or dark gray and fairly dark gray in itself – without a direction or structure. That are limestones. That`s no suprise, because the Isar comes from the northern „lime alps“.

Parallel light and dark bands are evidence of the deposition of calcareous mud (approx. 200 million years ago). Different kinds of colours are created through different kinds of minerals that are mixed in the stones.

White stones consist of pur lime. In the past this stones had been collected and burned in lime kilns so they could used to built walls or for whitwashing walls.

Stoned corals and clams, whose shells are preserved in limestone, prove that the calcareous sediment was deposited in a sea. Such stones are relatively easy to find. On some pink pebbles we can find white circles: stem segments of the sea lily, a marine animal. On a lot of stones we can also find white streaks. These are composed of calcite. They show us that the stone is a „tormented rock“. When the mountains of the alps got uplifted (started over 50 million years ago) the rock layers had been broken. Water containing lime seeped into the cracks and formed white streaks. 

We also can find gneiss. These foreign objects can be identified by their colorful, sometimes glittering crystal layers. Normaly this stones can be found in the central alps.

How do the pebbles come to Lenggries?

The ice, that layed over the alps 10,000 years ago, left them in the gravel of the Isar as a memento. In the upper layers of the glacier, the rocks migrated across what are now watersheds into our region. In greenish gneisses we often find red or grey points. These are cut crystals of the semi-precious stone garnet.