Montenegro is composed of sedimentary and volcanic rocks from the Paleozoic through the Cenozoic. The crystalline basement below is not easily accessible and thus poorly understood. The country is divided into three zones.
The Dalmatian-Herzegovinian Zone is southwestern Montenegro. A thick layer of Cretaceous, Paleocene and Eocene foraminiferal limestone forms the surface. It is separated by a break in deposition from Anisian age flysch and limestone, thin Ladinian volcano-sedimentary rock, Late Triassic carbonates and Jurassic neritic carbonates. It was first described in 1948 as the Old Montenegro Overthrust, and is also called the Dinaridic zone.
The Sarajevo Sigmoid is a belt of Mesozoic flysch units beginning in Albania and spanning central Montenegro toward the northwest. It consists of shallow marine Permian and Triassic platform carbonates and clastic rocks. In the east it is overthrust along the Durmitor Nappe.
The East Bosnian-Durmitor Block covers northern and eastern Montenegro. Mostly continental clastics, limestone and volcanic rocks originate from the Triassic. Below, separated by an unconformity, are Devonian nappe features in Paleozoic rocks including slightly metamorphosed fine-grained clastics. In the southeast there is an unusual granite body which may have resulted from uncommon in situ granitization. It is surrounded by metamorphic mafic rocks.
The limestone ares are karstified and there is an enormous amount of karst features, especially caves, but also numerous spectacular karst poljes. The country is drained by the Lim and Tara river systems, which meet the Drina River, flow through Bosnia and Herzegovina, into the Danube and finally into the Black Sea. In southern Montenegro streams flow toward the Adriatic Sea. So the country is separated by the European watershed. On both sides most of the area is drained underground due to the karstification. The largest lake in Montenegro and the Balkans is Skadarsko Jezero (Lake Scutari), which is actually a waterfille karst polje with the floor below sea level. 50 km long and 16 km wide it has a total surface area of 370 km², of which 60 % is in Montenegro, the rest in Albania.