“Geological Trail to Kobilji curek”

In the village of Rob, you can park your car at the shop (Rob 1). By the shop, there is also a Geological Island, where you can find a more detailed geological map and a bench consisting of five types of rocks that you become acquainted with when visiting the trail. The legend of the map is also written in Braille and the rocks can be touched. The stratigraphic sequence of rocks on the map shows the chronologic succession of the formation of a particular rock. You then take the Rob–Predgozd asphalt road past the sawmill (Walking Sawmill Rob) and turn left towards the macadam forest road to Kobilji curek, where an information board of the geological trail is located. There are also some parking spots next to the information board showing all the waypoints. Then follow the yellow-green metallic points of the Geological Trail to Kobilji curek, which is managed by the Parnas Institute, and learn more about the geological basis of the surrounding area of the village of Rob in the Lower Carniola and discover what the latter has to do with the Romans who controlled the area.

The geological composition of the Rob area can be considered as part of important natural heritage and was formed 200 to 245 million years ago. The trail follows the Kobilji curek Stream and leads to the waterfall of the same name. The oral tradition says that the Kobilji curek Waterfall was named after a hole that resembled a mare’s behind and through which water used to flow. Today, the water flows the other way since that hole was filled with rocks and branches. The trail is crossed by the 1,550 m long barrier of the claustra Alpium Iuliarum system, which operated between the second half of the 3^rd century and the beginning of the 5^th century. There are 10 checkpoints along the trail, which are marked with metallic numbers in yellow-green colour. Information boards are set up in three places.

At the confluence of the Kobilji curek Stream and the Črna voda Stream, two pure and clear streams meet, coming from a forested, uninhabited hinterland. After the confluence, the Robarica Stream is created, which in a downstream manner gives water to the marshy meadows in Veliki logi, home to marsh and bog plants and animals. A bit further from Rašica, it disappears underground and flows towards the Radensko polje Field and the spring of the Krka River.

The violet-red colour of sedimentary rocks and soil is mostly due to the presence of iron or ferrous minerals, especially hematite. The layers of sedimentary rocks were in a horizontal position at the time of formation, but today we can rarely observe horizontal layers. The tilting layers are the result of tectonic processes during which the layers were leaning, folding and breaking.

The hardness and sharpness of tuff were known already in the Old Stone Age. In that period, various primitive tools were made from tuff: scrapers, knives, drills and more. In addition to chert, tuff was the most common rock used by prehistoric man in our area.

The dark grey or black colour of limestone (as well as dolomite) is usually due to the presence of humus substances or bitumen. Even a small amount (less than 1%) of finely dispersed bitumen can colour the rock completely black.

Limestone is composed of calcium carbonate, more specifically of the mineral calcite, chemically CaCO₃. It is dissolved by carbonic acid, which is formed when the rainwater reacts with carbon dioxide. The layered limestone is arranged in level layers, while the surface of the non-layered limestone is irregular. The latter was used by the Romans in the construction of the Late Roman barrier system claustra Alpium Iuliarum.

Fossils are usually not found in all layers of rock. They are mostly present only in certain layers, where they appear in larger quantities, however. Persistence is thus required in the search for fossils. You can find a fossil site near the cart track. The fossils will be most easily observed with the help of a magnifying glass since they are mostly one millimetre in size. The fossil shells at this site are classified among the Posidonia wengensis species.

In the spring, we find numerous tadpoles and sometimes adult animals in the ruts and larger puddles along the stream. The alpine newt is an amphibian with a tail, similar in shape to a salamander, and has warning colours only on its belly. During the mating period, males are adorned with a blue line on their side, while females have dark colours over their entire bodies. After the end of the mating season, they leave the water and live in the forest beneath the stones and rotten wood.

The Late Roman barrier system claustra Alpium Iuliarum, which was probably built as early as in the second half of the 3^rd century, protected the heart of the Roman Empire. The barrier system consists of several sections of stonewalls, towers and forts, extending from Rijeka in Croatia to the Soča Valley in Slovenia. The section in front of you is special due to its floor plan, which bends for 90 degrees at the top of the Gradiški vrh Hill. It measures approximately 1,550 m in length and was once reinforced with seven towers. On the part damaged during the construction of the forest road, archaeologists and restorers from the Institute for the Protection of Cultural Heritage of Slovenia (ZVKDS) re-presented the cross-section of the wall in 2018. The wall consists of a walking lane with a screed and a higher parapet and is 2.40 m wide in this part.

Dolomite is both a mineral and a rock, composed of the mineral dolomite, which is chemically calcium magnesium carbonate. The chemical difference between limestone and dolomite is the reason that hydrochloric acid dissolves limestone but not dolomite. Diluted 10% hydrochloric acid is used for the test.

A special conservation regime applies to the Kobilji curek forest reserve (3 ha). At the end of the gorge, there is the Kobilji curek Waterfall, the highest waterfall in the Lower Carniola region. The waterfall has two steps, each about 15 m high. It falls completely over the limestone rock edge formed when the rock layers ruptured. Nearby, we find the Slovenian endemic flower, the Carniolan Primrose (Primula carniolica). It blooms from April or May until June.

Tufa is mostly formed around water springs. Chemically, tufa is calcium carbonate, the same as limestone. Its formation is a reverse chemical process of limestone dissolution. The formation of tufa usually requires aquatic plants that alter the chemical balance in spring water, enabling tufa to be secreted.

A meander is a river bend or curve. The water in the stream or river is always faster and stronger on the outer side of the meander, which is why it removes the rock material there and erodes the bank. On the inner side of the meander, however, the stream is weaker, which is why it deposits its sediments there in the form of a meander embankment.