The geological structure of Ojdula is completely covered by sedimentary rocks. The oldest rocks are of Cretaceous age (145 million years), which are mainly black shales (Audia strata). The cracks in these rocks are filled with extremely pure quartz crystals, which we know as "Ojdula diamonds" because of their rarity and beauty.

Next, in chronological order and extent, is the Tarkő sandstone. These rocks were deposited at the beginning of the Eocene (55-40 million years ago). The Kőlik cave (45 m) on the slope of Mount Csihányos, which was created by tectonic movements (geological structure), and the Kurta giant stone, which was prepared by erosion, are found in this rock type. Due to its workability and distribution, Tarkő sandstone is one of the main raw materials for construction in Ozsdola.

Our next larger rock units were deposited during the Oligocene (33 - 23 million years ago). These rocks have reached the center of attention from an economic point of view, through bituminous shales, as potential oil reservoirs. Oil, "finger", found in the Oituz Strait and the Salt Hill area, which was used by our ancestors for lubrication and car lighting, has been known for a long time. On the basis of these occurrences, as well as traces of oil (petroleum) appearing in the springs, in the last half of the 19th century a targeted research was started. In connection with this, several exploratory wells were drilled in the Ojdula area and in the Putna valley, but they did not prove to be as successful as in Gelencé. Oil shale alternates with Kliwa sandstone (high-purity quartz sandstone) and conglomerate (previously deposited and redeposited rocks). These rocks form the Kovás‐ponk and the Oituz valley.

During the geological periods described, sediments that were deposited and accumulated during tectonic movements were folded and organized into cover systems. As a result of subsequent movements and the release of stresses in the rocks, sediments were created, playing an important role in the formation of valleys and the water network. Crustal movements are still active today, as evidenced by frequent earthquakes.

Our youngest known geological formation is Quaternary peat (several thousand years old), which is found in the lowest part of Ojdula in Bokros. Peat is formed from the accumulation of dead plants in a watery, air-enclosed environment. The plant community of the peatland during landscaping and drainage, as well as with the subsequent extraction works, completely changed the character of the moorland that existed until then. After drying, it is used as fuel or as a soil conditioner.

At the end of my brief geological description, I would like to mention the soil formation that continues today, of which the most common types are brown forest soils, podzolized soils and chernozem.